Allow overwriting the src file with optimized

Fixes "Fatal error: ENOENT, no such file or directory" when src and dest are the same.
Merge pull request #28 from thetalecrafter/overwrite

Allow overwriting the src file with optimized version
Remove `-force` flag

It's not needed anymore and enables creating bigger files than the original.

Fixes #27
Limit image optimizations to 10 at a time

Closes #19
Fixes #13
Remove unneeded logic introduced in a PR

Closes #32

Should also fix #21 #31

Use dynamic mapping instead: https://github.com/gruntjs/grunt/wiki/Configuring-tasks#building-the-files-object-dynamically
0.1.3
Changelog
Fix exception when running in verbose mode

Forgot to add a child process check

Fixes #34
Changelog
0.1.4
Merge remote-tracking branch 'grunt/master'

Conflicts:
	README.md