Add Method to Generate Object From Source Directories
The method iterate_input iterates over the source directories making objects
out of the folders that will be useful later. The objects contain the absolute
path, the relative path, and whether the folder is at the supplied depth.

The depth option has the user specify how far into the source folder is the
level at which symlinks should be created for. With a directory structure like
music.flac/Artist/Album/, source_high would be music.flac and you would want to
create symlinks for the albums. That means --depth=2. If you linked to the
artist you could miss out on albums in different qualities.
Add Ability to Follow Symbolic Links in the Source Paths
The code before followed all paths regardless of whether they were symlinks or
not. Now there is an option (--followsymlinks) which enables this behavior. It
is disabled by default.

os.path.islink() returns false for symlinked folders if the path ends in /.
Add Documentation
Add document to to iterate_input and mmirror.
Update iterate_input's Recursive Base Case
Move the base case up a level. It's already known by the at_depth value
whether another call needs to be made.