force all string arguments to be converted to html-safe before use

use ERB::Util.h and add note to the README

Closes Issue #2
use inject to build html_safe_options
Merge pull request #3 from rdunlop/html_safe_arguments

force all string arguments to be converted to html-safe before use
Bump version to 0.4.0
Only escape HTML in string parameters

Escaping all values converted them to strings prematurely, which caused 
a regression when dealing with specific parameters, such as `count` for 
I18n’s pluralization handling.
Bump version to 0.4.1