Add options method, tablespace to create index

Index method and tablespace is very useful.
Add index method (USING btree, for example) and tablespace according to CREATE INDEX expression in postgresql documentation.

http://www.postgresql.org/docs/9.3/static/sql-createindex.html
Update schema.moon
Merge pull request #83 from dant4z/patch-1

Add index method and tablespace to create index