Update documentation

[glensc]

1. Direct user to readme from run list view, rather having instructions duplicated
2. Update xhgui releases link (preinheimer -> perftools)
3. Briefly describe how php-profiling works and how to import jsonlines files.
4. Remove extension install instructions (profiling data is not the goal of this project)
5. Update profiling logic to be abstract and how to do offline profiling
6. Remove ext-dom phpunit requirement (the list IMHO incomplete, and phpunit is not required for application run)
7. Move file saver block: Update file saver documentation php-profiler#19
8. Move profiling.enable docs: Import profiler.enable documentation from xhgui project php-profiler#20
9. Move profile.simple_url docs: Import simple url config from xhgui readme php-profiler#22
10. Move ignored_functions docs: Import ignored_functions from xhgui documentation php-profiler#23

[glensc]

@markstory what is the proper capitalization of XHGUI? I want to be consistent in the documentation.

1. XHGui
2. XHGUI
3. Xhgui

[glensc]

the rewritten file saver block documentation in profiler package: perftools/php-profiler#19

[glensc]

Moving profiling.enable docs: perftools/php-profiler#20

[markstory]

what is the proper capitalization of XHGUI?

I've tried to use XHGui in the past, but we can always change it if that is an oddly shaped word.

[glensc]

there are profiler related config options in this project:

config/config.default.php:    'profiler.options' => array(),

these should be removed from here, but not sure when :)

[glensc]

This is in my opinion good enough to merge. @perftools/maintainers @Krinkle WDYT?

[Krinkle]

LGTM. Also +1 for "XHGui" as the canonical spelling I've personally used/preferred.