add --include/--exclude flags, with correct precedence

On rg 0.8.0 / OS X 10.12.6

When using `rg -Tfiletype -tfiletype foo`, the exclude takes precedence over the include. Is this intentional behavior?

My use case is a `.ripgreprc` which excludes minified files by default, which I do occasionally need to search. I can do `rg --type-add=minified:*.min.{css,js} -tminified --no-config foo` in this case, but this is pretty clunky. I would much rather do `rg -tminified foo` and have my include clobber my config file's default exclude.

Start by reproducing the reported `rg -Tfiletype -tfiletype foo` behavior and compare it with the `.ripgreprc` use case described in the issue. Trace how command-line type includes and excludes are combined with configuration, then add coverage showing the intended precedence and verify the minified-file workflow.

Written by the indexing model from the issue text.