Toggle Stemming

Modified a few things in the library, specifically the Analyzer constructor in `plan.go` and the ParseQuery function in `searcher.go`.  Certain functions will now take a boolean parameter to toggle stemming.  I generalized the Analyzer struct to use a pointer to a generic Analyzer rather than a EasyAnalyzer as well.

Also had to import a few more C headers into `plan.go` and `searcher.go` and tried my best to clean up references to prevent memory leaks with the data structures that I introduced into the code.

Obviously, any existing code that uses this library may have a few things break because of the additional function parameters, so I wonder if there is a better way to go about doing this.