Improved perf data bars to handle more types of perfdata

Updated the logic that builds the perfdata bars to be able to handle almost all of the thresholds specified in the Nagios Plugins Development Guidlines. The only thing these changes don't support is when the '@' symbol is used to do inclusive thresholds. Another thing to note is that the regex to pull apart data was not only modified to handle these other thresholds but to also allow the UOM to be any number of characters long. Previously, this was limited to only allowing two characters however there isn't anything in the guidelines that talks about the max length the UOM can be.
Updated perfdata regex used for perfbars

The regex from the last commit had some flaws with how it handled UOM, negative numbers and decimals. This is a much more complicated regex but should hopefully correct the issues to make the matching work as one would expect. Also changed logic slightly to handle undefined elements better.
Merge pull request #225 from awiddersheim/master

Improved perf data bars to handle more types of perfdata