Support for ENUM-columns, Decimal-Precision & Multiple Indexes/Options in MigrationGenerator

ENUMs can now be created via --fields="someStatus:enum['accepted', 'rejected', 'revoked']"

Decimal-Precision can now be set via --fields="price:decimal[10,2]"

Multiple indexes/options can now be set like --fields="hash:string[32]:nullable:unique"


Side Note: This patch makes pull-requests #142, #107, #104 and #72 effectively redundant, as the new field parsing also covers the handling of decimal-precision specification, enum values & indexes.

Addresses issues #70, #89,