Convention for db mappings

[ersran9]

Currently the mappings are as is.

The naming convention to be followed is:
TableName : table_name
bigColName: big_col_name
"ix": 'ix_%(column_0_label)s',
"uq": "uq_%(table_name)s_%(column_0_name)s",
"ck": "ck_%(table_name)s_%(constraint_name)s",
"fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
"pk": "pk_%(table_name)s"

On top of this, user can override by using table and column alias which already exists.
related issue #4