Update schema classes to return a hash.

This will make adding fixed length strings much easier.
Add support for fixed length strings.

This flag is useful for indicating the difference between varchar + char
fields. In some databases (mysql) the performance characteristics
between char & varchar are important.
UUID fields should also be fixed length strings.

Since we can't preserve the UUID type a fixed length string will have to
do.
Merge pull request #1262 from markstory/3.0-char-fixed

3.0 Add support for fixed length strings.