analyzer action

Adds analyzer action which allows individual targets in a scheme to be
analyzed. The action will run a regular build prior to running analysis.
It pulls analyzer results from the generated plist files instead of the
compiler output, thus allowing for incremental analyzer runs.
Merge pull request #78 from facebook/yiding/analyze-action

Added an analyzer action which allows for select targets in a scheme to be analyzed.
It also pulls analyzer results from the plist files rather than stderr, this makes it so incremental changes only requires incremental re-analyze. The results come out at the end of the run as special structured reporter events.