Filter for yaml/yml files in source directories

[atrocities]

The Conjure IR compiler attempts to compile any file in a given directory when a directory is specified as an input. This includes non-Conjure sourcefiles, like swapfiles left behind by an editor.

What did you want to happen?

More desirable behavior might include:

• Only compiling things with a .yml/.yaml extension
• Ignoring hidden files in source directories
• Making it possible to pass in a list of sourcefiles when there is more than 1 source file. This way the build tool can enumerate the files that need to be built.

[carterkozak]

Enforcing the yml extension sounds reasonable, would you like to submit a patch?

[nmiyake]

Dupe of #69