Make WebOptimizerCache dir path customizable

[dandros]

I would prefer instead of /obj/WebOptimizerCache to have just /cache folder. or /cache/weboptimizer

What's the purpose of build LigerShark.WebOptimizer.Core.targets ? I understand that cache is generated on runtime anyway.

[cramhead]

Having a memory cache option would also be good, as there are no file permissions to deal with. When deploying I need to make sure to obj/WebOptimizerCache folder and set write permissions

[hellfirehd]

@cramhead, there is a memory cache, but it's not an option (yet). See here.

[hellfirehd]

@madskristensen PR #80 closes this.

@cramhead Memory caching and Disk caching can now be enabled/disabled separately.