Include ability to omit directories

[object88]

Langd is hardcoded to skip all directories that begin with . (i.e., .git). It would be helpful to be able to specify one or more globs to additionally omit (i.e., testdata, or **/foo.

[object88]

Need to expose this as a setting.

[object88]

testdata is automatically excluded now, but still want to provide a way to customize this.