Added the ability to have certain query string parameters excluded from the cache key

[lazytom]

sometimes one might want to exclude certain query string parameters from
the cache key, e.g. when using a qs parameter as a cache buster for a
CDN, etc.

added the ability to do this via a config item:

<ignoredquerystringparameters parameternames="" />

the parameternames attribute accepts a comma-delimited list of parameter
names that will be ignored by internal processing (and thus also from
the cache key)

[lilith]

Thanks for the pull request!

Currently all new development is happening on the develop branch. I can merge an updated pull request that:

1. Exposes the configuration via IPipelineConfig and PipelineConfig: https://github.com/imazen/resizer/blob/master/Core/Configuration/PipelineConfig.c (caching is suggested, as this executes for every HTTP request going through the server).

2. Targets the 'develop' branch - which should also have correct NuGet handling.

3. Uses the existing "pipeline" XML element - "pipeline.dropQuerystringKeys" would probably be best.

4. Applies to both InterceptModule and AsyncInterceptModule