Support nested directories

[Seanstoppable]

Common strategy is to have a 'schema' directory in the root of a repository.

However, using sem-add from the root puts the file in /scripts, rather than /schema/scripts

[mbryzek]

One implementation of this would be to look for a:

".sem"

configuration file in the current working directory. If found, read the configuration and in there we'd have one key:

scripts_dir=./schema/scripts

By default this would be "./scripts" for backwards compatibility.

Any other thoughts for possible implementation?

[Seanstoppable]

Yeah, that was essentially my thought.