Update symbol transformation syntax

Use 2.0 syntax for a subjectively simpler and more transparent transformation.

#ignore
Use version 1.8 of ruby for bundle items

10.7 and 10.8 only include ruby 1.8, so all bundle items have been written to work with that. Optionally supporting ruby 1.9 and 2.0 is problematic as these versions are not fully backwards compatible.

#ignore
Added MathJax support to Markdown preview

Disabled by default, to enable support set a 'TM_MARKDOWN_MATHJAX' variable to '1' in preferences.
Merge branch 'master' of https://github.com/textmate/markdown.tmbundle

# By Allan Odgaard (1) and others
# Via Michael Sheets
* 'master' of https://github.com/textmate/markdown.tmbundle:
  Added MathJax support to Markdown preview
  Use version 1.8 of ruby for bundle items
  Update symbol transformation syntax