Adding custom sanitizers and custom trim tags

• Adding the option to provide custom sanitizer functions.
• Adding the option to provide custom characters to the trim sanitizer.

Fix string "title" behavior for characters with punctuation marks

Fixes #11 by changing behavior of the "title" tag to first lowercase the entire string, then use Go's built in strings.Title function. This maintains the existing behavior of lowercasing every character except the first in each word but also prevents characters like á from causing the string to be split into multiple words.

First release

v1.0.0

added maximum size for slices (#10)