Multiple options

I often need to leave more than one option on a scheme during the migration build.  For example an item might be require ->index()->nullable(); and the current version only allows for one option, the rest are ignored.  These changes allow for multiple options.  I updated the MigrationGenerator.php script as well as the docs.  I am new to submitting changes through git and github.  I ammended the commit as I forgot to save a file but somehow I have three commits...sorry.