Allow filtering of sweepers using regular expressions

[SarahFrench]

Fixes #74

This PR allows users to filter sweepers using regular expressions. Currently if a user uses ^aws_foo$ as a filter it will look for a sweeper whose name contains the string "^aws_foo$". Now the string will be interpreted as a regex.

TODO:

• address valid use of commas in regex: quantifiers like {1,3} or {1,}