Add ability to generate migration files without db interaction from CLI

This functionality only works when arguments are passed to the command `cake Migrations.migration generate`.

This commit adds the ability to perform commands such as the following:

    app/Console/cake Migrations.migration generate create_users id:primary_key name:string created modified

    app/Console/cake Migrations.migration generate alter_users name:string:index

    app/Console/cake Migrations.migration generate drop_users

    app/Console/cake Migrations.migration generate add_taxonomic_stuff_to_posts category:string tags:string

    app/Console/cake Migrations.migration generate remove_taxonomic_stuff_from_posts category tags

The above commands would:

- Create a users table with the fields [`id`, `name`, `created`, `modified`]. A single primary key index would exist on `id`, and the `created` and `modified` fields would default to `datetime`, as per CakePHP conventions. Since the type is specified on `name`, it is string.
- Add an index to the `name` column in the `users` table.
- Drop the users table.
- Add `category` and `tags` fields to the `posts` table.
- Remove `category` and `tags` fields from the `posts` table.

Due to the conventions, not all schema changes can be performed via these shell commands.

Migration Names can follow any of the following regices:

- *create_table* `/^(create)_(.*)/`: Creates the specified table
- *drop_table* `/^(drop)_(.*)/`: Drops the specified table. Ignores specified field arguments.
- *add_field* `/^(add)_.*_(?:to)_(.*)/`: Adds fields to the specified table
- *remove_field* `/^(remove)_.*_(?:from)_(.*)/`: Removes fields from the specified table
- *alter_table* `/^(alter)_(.*)/` : Alters the specified table. The *alter_table* command can be used as an alias for `create_table` and `add_field`.

Migration names are used as migration class names, and thus may collide with other migrations if the class names are not unique. In this case, it may be necessary to manually override the name at a later date, or simply change the name you are specifying.

Fields are verified via the following the following regular expression:

    /^(\w*)(?::(\w*))?(?::(\w*))?(?::(\w*))?/

They follow the format:

    field:fieldType:indexType:indexName

For instance, the following are all valid ways of specifying the primary key `id`:

- `id:primary_key`
- `id:primary_key:primary`
- `id:integer:primary`
- `id:integer:primary:ID_INDEX`

Field types are specific to the database connection in use specified by the `--connection` argument (`default` by default). Thus, valid `Postgres` field types include `inet` and `number`, while for `MySQL` the fieldType would be ignored.

There are some heuristics to choosing fieldtypes when left unspecified or set to an invalid value:

- `id`: *integer*
- `created`, `modified`, `updated`: *datetime*
- Default *string*

Lengths for certain columns are also defaulted:

- *string*: `255`
- *integer*: `11`
- *biginteger*: `20`
fix failing test - testGenerateDump

Cake standards expect true, false and null to be lowercase. The code was being generated correctly (lowercase), but was being asserted against an incorrect example (which used uppercase NULL)

Signed-off-by: Joshua Paling <joshua.paling@gmail.com>
Fix failing test - testRun

The test was failing due to the assertion on line 238, where it expected 'reset' => true to exist in the array - but there's no situation where that key/value is added, or needs to be added, in the code itself. Reset works, and asserting that 'version' => 0 is sufficient to test this.

Signed-off-by: Joshua Paling <joshua.paling@gmail.com>
refactor - break up 80+ line method

generate() method was 80+ lines and very hard to read. To break it up, I had to pass several params in by reference to each sub-method, which isn't ideal either, but still an improvement in terms of readability.

Signed-off-by: Joshua Paling <joshua.paling@gmail.com>
fix whitespace coding standards

Signed-off-by: Joshua Paling <joshua.paling@gmail.com>
refactor & implement test for 'create table' and 'drop table' from cli arguments

Signed-off-by: Joshua Paling <joshua.paling@gmail.com>
implement code & test for 'remove fields' from cli arguments

Signed-off-by: Joshua Paling <joshua.paling@gmail.com>
implement code & test for 'add fields' from cli arguments

Signed-off-by: Joshua Paling <joshua.paling@gmail.com>
Merge pull request #148 from joshuapaling/feature/migrations-from-cli

Get migrations from cli working and tested.
Merge branch 'refs/heads/feature/migrations-from-cli' into develop