Remove trailing spaces in generated migrations

Cleanup trailing spaces that get inserted into each generated migration
file.
Merge pull request #15 from loganlinn/cleanup-trailing-whitespace

Remove trailing spaces in generated migrations
Move config-related logic into separate namespace

Previously, this logic lived in the core namespace.
This is motivated by the desire to add better error
messages around missing config parameters.
Check for missing required params in migrate config
Merge pull request #20 from maxbrunsfeld/check-required-config-params

Add informative message for missing params in migrate-config
arg parser
add a parser to the arg specs
specify a config function from the command line, let the config init function modify the migration config
throw an exception if config function can't be found