Combining (adding, subtracting) multiple language scopes

[alexpovel]

Currently, as of 07f4eb9, we can ask for e.g. srgn --python strings, meaning a single language scope. It would be neat to support passing multiple, which are OR'd together:

srgn --python strings --python comments 'thing'
# Alternate syntax
srgn --python strings comments

and also some logic for subtraction, which would work like normal set logic:

srgn --python class --not-python methods 'whatever'

which would match all contents of Python class bodies expect for those of methods.

As a feature, this wouldn't be too complex and unlock a whole new dimension of querying (while remaining dead simple).

[alexpovel]

Will implement 'subtraction' at a later date.