Clean gemspec/gemfile and add preliminary PrawnPDF formatter test suite

[64kramsystem]

• remove support for ancient rubygems version (1.2.0, from 2008)
• remove rake gem requirement in the Gemfile, since it's already in the gemfile
• remove the pdf-writer dependency, since the PDF formatter is gone
• downgrade Prawn version, until the test suite is fully restored
• add preliminary PrawnPDF formatter test suite

Closes #50; closes #23.

[64kramsystem]

@Odaeus so! I've done a bit of work with the gemspec and the test suite. there was no test suite for prawn pdf rendering, so I've started a preliminary test suite.
The prawn dependency needs to stay unfortunately to the previous, very old, version 0.12.0 😭 I will slowly extend the test suite to have reasonable coverage, then I'll have a look again.

[coveralls]

Pull Request Test Coverage Report for Build 63

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 580 unchanged lines in 11 files lost coverage.
• Overall coverage decreased (-60.4%) to 37.115%

---

Files with Coverage Reduction	New Missed Lines	%
lib/ruport.rb	4	38.46%
lib/ruport/formatter/template.rb	8	42.86%
lib/ruport/data/feeder.rb	11	35.29%
lib/ruport/formatter.rb	25	57.14%
lib/ruport/formatter/csv.rb	31	37.25%
lib/ruport/formatter/html.rb	32	34.55%
lib/ruport/data/record.rb	43	39.19%
lib/ruport/formatter/text.rb	54	27.63%
lib/ruport/data/grouping.rb	66	36.94%
lib/ruport/controller.rb	78	47.77%

Totals
Change from base Build 54:	-60.4%
Covered Lines:	386
Relevant Lines:	1040

---

💛 - Coveralls

[64kramsystem]

@Odaeus ok, I've removed the PrawnPDF formatter "placeholder" unit tests (the broken ones; there are a few working ones, and the new smoke test with real PDF data), so this PR is ready.

I've moved the broken ones into a separate branch; I'll repair them, and create a separate PR.

[kbrock]

Nice small set or changes.

Improving the gemspec and test coverage

[kbrock]

kicking it to run again.

in prep of merging

[kbrock]

Thanks for the great change @saveriomiroddi
Sorry for the delay