Optimize unsigned columns

[willvincent]

Any unsignable datatype that has the unsigned modifier specified will be optimized to it's unsigned[type] corresponding datatype.

ie:

foo: integer unsigned

Becomes:

$table->unsignedInteger('foo');

And so forth.

Closes #5

[jasonmccreary]

Very nice. Are there any others you think, beyond unsigned?

[willvincent]

Guess there are a couple nullable too.. nothing else jumps out at me. Let me get those added though

[willvincent]

Omitted nullableTimestamps() as that's the same as timestamps() and arguable less optimal :)

[willvincent]

Good call.. Str::startsWith is more readable

[jasonmccreary]

Yeah. I'll likely optimize the continue as well, but this is a great start.