Fix building error with 1.9.3

The commit 96802e9b0de4 forgot to add coding statements at the very
top of the file. This commit fix the test suite for 1.9.3 which failed
on both MRI and Rubinius.
Add MRI 2.0.0 to the Travis matrix
Remove RDiscount from the benchmark suite

Since RDiscount isn't supported on 1.9.2, we can remove it from
the benchmarks to ensure Redcarpet is compatible with 1.9.2
Update the date in the gemspec
Generalize gitignores.

Allows for easier extension building inside a submodule.
Update missing gitignore entry.
Merge pull request #250 from djanowski/patch-2

Update missing gitignore entry.
Add license to the gemfile
Merge pull request #251 from dnagir/patch-1

Add license to the gemfile
Cosmetic changes in the README [ci skip]
Ensure code spans put in emphasis work correctly

When putting code span into simple or double emphasis, we've got an
unexpected output. This commit fix this problem simply removing an
ignore statement about back ticks in the find_emph_char function

Fix #135 and #190
Merge pull request #252 from vmg/nested-code-emphasis

Ensure code spans put in emphasis work correctly
Ensure nested parenthesis are handled into links

Make sure that parenthesis inside the link's url are correctly parsed
Redcarpet considered the first ")" occurrence as the link's end so we
first count the number of open "(" and decrement this number each
time we found a ")".

Close issue #237
Merge pull request #258 from vmg/nested-parenthesis-links

Ensure nested parenthesis are handled into links
correct `render_man.rb` filepath
Merge pull request #259 from suan/patch-1

correct `render_man.rb` filepath
Optional highlight support
`<mark>`!
Changelog entry for highlight
Merge pull request #263 from soffes/highlight

Optional highlight support