Optimize Mysql::describe($model) with SHOW CREATE TABLE

Though "SHOW  FULL COLUMNS FROM $table" is convenient, for whatever reason it is not very fast. Using "SHOW CREATE TABLE $table" is very fast, though not directly convenient. I updated Mysql->describe($model) to use the output from SHOW CREATE TABLE by parsing it with a regular expression. The Model tests are a little over 10% faster on my system.