Change plugin loading logic to allow plugin overriding

Now, the plugin logic works like this:
1. Scan all specified plugin paths for any plugins
2. Group plugins by their name, and sort by descending version number
3. For each plugin name, go down the list of plugins until one is
   successfully loaded

Also handles things like plugins that are incompatible with current
core version (it won't load these), and plugins without versions (it
will give these lowest precedent, but will load them.)
Merge pull request #125 from adobe-photoshop/jrb/load-latest-plugin

Change plugin loading logic to allow plugin overriding
bump to v2.0.1-dev
add warning messages if incompatible/no plugins found
improve plugin loading error message
Update README.md

We shipped already!
set process title to generator
bump patch version number
Fix race condition where multiple messages with the same ID
were sometimes dropped.
Revert "set process title to generator"

This causes problems when node is launched as a subprocess of PS on mac.

This reverts commit dae9778fc22237cb7d129e7c84a6fe3f62424d2c.
Merge branch 'jrb/race' into ps-next