* Changed `Load` to `Unmarshal`
* made `Marshal` and `Unmarshal` into methods of `COF`
* added `New` function which creates a new, empty COF instance
* added helper functions `Marshal` and `Unmarshal`
* Changed `StreamReader.ReadBytes` to account for edge case of reading 0
bytes (this was returning an error when it should not have)
* added really simple unit tests for COF
*`StreamReader.Read` methods now return errors
The other edits in this commit are related to cleaning up lint errors
caused by the changes to StreamReader
* move music path enumerations into d2resource
* move text dictionary (.tbl) loader into d2fileformats sub-package d2tbl
* lint fix, add doc file for d2tbl
* moved data_dictionary.go into d2fileformats sub-package d2txt, added doc file
* added sub-packages d2geom for geometry-related things, and d2path for path-related things
* moved calcstring.go to d2calculation
* move bitmuncher, bitstream, stream reader/writer from d2common into sub-package d2datautils
* fix lint errors in d2datadict loaders (caused by moving stuf around in d2common)
* move size.go into d2geom
* move d2common/cache.go into sub-package d2common/d2cache
* renamed d2debugutil to d2util, moved utility functions from d2common into d2util
