Support Web IDE Library file structure.

[technobly]

Had an issue where a user was compiling a project that contained a Spark Library... which had a lib/ subfolder full of source and header files.
http://community.spark.io/t/spark-dev-editor-problem/8009

It would be great to support this file structure natively so users do not have to manage two different sets of files. However some Spark Libraries contain multiple examples, so this may not be completely possible. At the lease we should ignore the config files (spark.json, readme.md, etc..), and support subdirectories.

[suda]

We have two kinds of problems here:

1. Supporting nested directories in projects
2. Ability to specify entry point.

First one can be easily fixed (I'll get on that) but second one is more complicated, so I propose to move discussion about it to #14