Explicitly add GPL v3 license and release v0.1.0

Update project description

When this library was started, it was only meant for string differences.
However, the functions have since been genericized, so they work on any
types that can be compared!

Add summary documentation comment

Improve documentation strings

Add prettyDiff proc for creating formatted diff

Add example diff application

Add note about adding convenience wrappers

Implement simplediff in Nim along with stringDiff wrapper