Add information about Jakub's installation screencast

Jakub Ostrowski has created a great screencast showing MESA
installation.  Add this to the news and link it from the prereqs page.
Added a parser for MESA defaults files

A future version of MESA will include defaults files which will be
formatted according to a set of (in-progress) formatting guidelines.

This adds a script which can parse these files into markdown, which can
then be included into the main MESA site.  It requires the parslet gem.
Chomp paragraph symbols off of anchors
Refactor parsing scripts

The parser remains in defaultsParser.rb.  This moves the script that
transforms the parse tree into Markdown into markdownTransformer.rb.

A script that uses these to parse the MESA defaults files is included in
make_docs.rb.
Update pages that display defaults files

This removes the old defaults pages and the hacks that were needed to
get them working.  It adds individual pages for each of the new defaults
files.
Fix parser definition of "option"

In pgstar.defaults, an option can look like foo(:,:)
Drop trailing comments

This allows pgstar.defaults to be rendered as-is