Align td and th with css instead of align property

When you align tables with css, <td align="..."> gets overridden.
Using inline styles keeps alignment no matter what CSS contains.
Suppress compiler warnings
Fix #57 -- SmartyPants handling of single quotes.
Correct output when single quote is NOT being converted

E.g. if the original text is "test'test".
Fix compile error in C code
Add option to ignore usual indented code blocks.

Markdown converts text with four spaces at the front of each line to
code blocks. Of course we should support that, but when using fenced
code blocks, indented one can even be harmful. There should be a way to
turn them off.

This patch adds option to disable indented code blocks.
test that links with quotes work
Add optional underline support
This is `*italic*` and this is `_underline_` when enabled.
Remove unnecessary function pointer
Merge pull request #226 from grosser/links_with_quotes

test that links with quotes work
Add underline to readme
Merge pull request #227 from soffes/underline

Add optional underline support
Mark all symbols as hidden except the main entry point

This avoids conflicts with other gems that may have some of the
same symbols, such as escape_utils which also uses houdini.
Merge pull request #229 from tomhughes/visibility

Mark all symbols as hidden except the main entry point
Add a CHANGELOG file

The changelog file contains all changes which aren't cosmetic
Ensure StripDown render adds new line characters

This commit fix #175. When using the StripDown render, special new
lines characters (\n) weren't added for paragraphs. Also enable this
for headers.

Add simple tests to ensure the creation of these new lines.
Merge pull request #234 from vmg/stripdown_fix

Ensure StripDown render adds new line characters
Add a basic benchmark file

Fix the benchmark rake task which was useless adding a super simple
benchmarking file measuring performances with other markdown parsers:

  * Kramdown
  * BlueCloth
  * RDiscount

Results example of the benchmark:

              user        system      total         real
Redcarpet   1.780000     0.010000   1.790000     (1.802302)
BlueCoth    14.150000    0.050000   14.200000    (14.515556)
RDiscount   6.970000     0.060000   7.030000     (7.147544)
Kramdown    320.840000   1.610000   322.450000   (325.181537)
Merge pull request #200 locally

Conflicts:
	ext/redcarpet/buffer.h
Add a changelog entry for d949cbddb2