Resolves issue #78

[ixti]

Improves the way strings are got sluggized in order to resolve #78
This is re-open of pull request #96 due to some strange problems with pull request range update.

[ixti]

I believe patch is obvious enough, but still I will comment it:

• trailing and leading dashes are removed, e.g.: -foo-bar- become foo-bar
• & become -and-, e.g. Rock&Roll become rock-and-roll
• /[\s.,!?_+=]/+ become -, e.g. Foo!Bar? become foo-bar
• other chars except alphanumeric and dashes are removed, e.g. 1st << day >> become 1st-day
• dashes are got squeeze, e.g. abc--^^--def become abc-def