Implemented resolving of relative module names to absolute paths

[ichernev]

Specifying files to mock by a relative name is not enough if you require the same file multiple times from different directories. So I added an option to mockery to convert all relative filenames to absolute ones, based on the test file for example. There are two advantages of doing so:

1. You can specify the filenames to mock, relative to the test file -- i.e the same way requires work, so its a no-brainer
2. Requiring the same file from multiple locations would return the given mock, because all filenames are converted to absolute ones when requiring

[benbuckman]

+1

[benbuckman]

I wonder, couldn't this be done more simply, with path.resolve or require.resolve on all entries to registeredMocks? (Probably as an option in registerMock)