* Initial work on refactoring the font metric code

- Moved away from the archaic method of writing out PHP to a file and including it in the next run, by writing out the metrics data as JSON and reading from the file as required.
- General tidying up of code and trying to make sense of the > character 127 processing, and why we're doing what we're doing.
- For some reason, character widths appear to be broken for characters > 127 when reading the 127 file - when the file doesn't exist and we process on-the-fly, the widths appear to be OK. Hmmz.

* A bunch of reactors and cleanup around writing and accessing the font metrics and character widths files

* Fix to generate_unicode_font_specs, to ensure that we are actually outputting the correct font - reset() doesn't like operating on the results of explode() directly
Updated PDF.php to ensure that font metrics files get written with .php extension - aborted the JSON path!
Changed some of the variable naming conventions back to their original values in PDF.php, because of the side-effect of these variables not existing in the resulting file (boo, more refactor needed)

* Merge branch 'master' of github.com:DocnetUK/tfpdf into font_metrics_refactor

# Conflicts:
#	src/font/unifont/babelstonehan-bold-font-metrics.json
#	src/font/unifont/babelstonehan-bold-font-metrics.php
#	src/font/unifont/babelstonehan-bold.mtx.php
#	src/font/unifont/babelstonehan-bolditalic-font-metrics.json
#	src/font/unifont/babelstonehan-bolditalic-font-metrics.php
#	src/font/unifont/babelstonehan-bolditalic.mtx.php
#	src/font/unifont/babelstonehan-font-metrics.json
#	src/font/unifont/babelstonehan-font-metrics.php
#	src/font/unifont/babelstonehan-italic-font-metrics.json
#	src/font/unifont/babelstonehan-italic-font-metrics.php
#	src/font/unifont/babelstonehan-italic.mtx.php
#	src/font/unifont/babelstonehan.mtx.php
#	src/font/unifont/dejavusans-bold-font-metrics.json
#	src/font/unifont/dejavusans-bold-font-metrics.php
#	src/font/unifont/dejavusans-bold.mtx.php
#	src/font/unifont/dejavusans-boldoblique-font-metrics.json
#	src/font/unifont/dejavusans-boldoblique-font-metrics.php
#	src/font/unifont/dejavusans-boldoblique.mtx.php
#	src/font/unifont/dejavusans-extralight-font-metrics.json
#	src/font/unifont/dejavusans-extralight-font-metrics.php
#	src/font/unifont/dejavusans-extralight.mtx.php
#	src/font/unifont/dejavusans-oblique-font-metrics.json
#	src/font/unifont/dejavusans-oblique-font-metrics.php
#	src/font/unifont/dejavusans-oblique.mtx.php
#	src/font/unifont/dejavusanscondensed-bold-font-metrics.json
#	src/font/unifont/dejavusanscondensed-bold-font-metrics.php
#	src/font/unifont/dejavusanscondensed-bold.mtx.php
#	src/font/unifont/dejavusanscondensed-boldoblique-font-metrics.json
#	src/font/unifont/dejavusanscondensed-boldoblique-font-metrics.php
#	src/font/unifont/dejavusanscondensed-boldoblique.mtx.php
#	src/font/unifont/dejavusanscondensed-font-metrics.json
#	src/font/unifont/dejavusanscondensed-font-metrics.php
#	src/font/unifont/dejavusanscondensed-oblique-font-metrics.json
#	src/font/unifont/dejavusanscondensed-oblique-font-metrics.php
#	src/font/unifont/dejavusanscondensed-oblique.mtx.php
#	src/font/unifont/dejavusanscondensed.mtx.php
#	src/font/unifont/dejavusansmono-bold-font-metrics.json
#	src/font/unifont/dejavusansmono-bold-font-metrics.php
#	src/font/unifont/dejavusansmono-bold.mtx.php
#	src/font/unifont/dejavusansmono-boldoblique-font-metrics.json
#	src/font/unifont/dejavusansmono-boldoblique-font-metrics.php
#	src/font/unifont/dejavusansmono-boldoblique.mtx.php
#	src/font/unifont/dejavusansmono-font-metrics.json
#	src/font/unifont/dejavusansmono-font-metrics.php
#	src/font/unifont/dejavusansmono-oblique-font-metrics.json
#	src/font/unifont/dejavusansmono-oblique-font-metrics.php
#	src/font/unifont/dejavusansmono-oblique.mtx.php
#	src/font/unifont/dejavusansmono.mtx.php
#	src/font/unifont/dejavuserif-bold-font-metrics.json
#	src/font/unifont/dejavuserif-bold-font-metrics.php
#	src/font/unifont/dejavuserif-bold.mtx.php
#	src/font/unifont/dejavuserif-bolditalic-font-metrics.json
#	src/font/unifont/dejavuserif-bolditalic-font-metrics.php
#	src/font/unifont/dejavuserif-bolditalic.mtx.php
#	src/font/unifont/dejavuserif-font-metrics.json
#	src/font/unifont/dejavuserif-font-metrics.php
#	src/font/unifont/dejavuserif-italic-font-metrics.json
#	src/font/unifont/dejavuserif-italic-font-metrics.php
#	src/font/unifont/dejavuserif-italic.mtx.php
#	src/font/unifont/dejavuserif.mtx.php
#	src/font/unifont/dejavuserifcondensed-bold-font-metrics.json
#	src/font/unifont/dejavuserifcondensed-bold-font-metrics.php
#	src/font/unifont/dejavuserifcondensed-bold.mtx.php
#	src/font/unifont/dejavuserifcondensed-bolditalic-font-metrics.json
#	src/font/unifont/dejavuserifcondensed-bolditalic-font-metrics.php
#	src/font/unifont/dejavuserifcondensed-bolditalic.mtx.php
#	src/font/unifont/dejavuserifcondensed-font-metrics.json
#	src/font/unifont/dejavuserifcondensed-font-metrics.php
#	src/font/unifont/dejavuserifcondensed-italic-font-metrics.json
#	src/font/unifont/dejavuserifcondensed-italic-font-metrics.php
#	src/font/unifont/dejavuserifcondensed-italic.mtx.php
#	src/font/unifont/dejavuserifcondensed.mtx.php
#	src/tFPDF/PDF.php