Removes the __del__ override

Removes the __del__ override in AbstractCoverage - causes memory leaks when circular references are present, which they are, primarily with ParameterFunctions

Locks the 'inline_data_writes' attribute to True: Removal of the __del__ method broke some aspects of the out-of-band
brick writing methodology…no biggie at this point because it's not being
used!
Replaces use of RTree library

Encountering segmentation faults from the RTree library after removing
the __del__ override.  Replaces its use with the RTreeProxy class - a simplified, python-only code for linear searching (only works for 1D!)
Updates (minor) to tests after mem leak fixes
Merge pull request #84 from blazetopher/fix_mem_leak

Fixes memory leak