Word correction

Just a little word correction.
Prevents calling table seeders more than once
Added a check in SeedGenerator to see if the call to the table seeder has already been appended to DatabaseSeeder.php. It's useful if you're re-running your generators.
Merge pull request #192 from marlek/limiting-seeder-append

Prevents calling table seeders more than once
Merge pull request #160 from jojovem/master

Word correction
Update readme.md
Fixed the spelling of through in the readme
Merge pull request #195 from GrahamCampbell/fix-readme

Fixed the spelling of through in the readme