- Factors out (and deprecates) `Command`
- Deprecates certain free functions
- Adds better error handling
- Adds more free functions
- Refactors file handling
- Improves documentation
Notes on file loading (and general file handlers):
The interpreter command `.L` will load files but appears to not fail if
the file isn't source code or a library.
Calling `gSystem->Load()` will load a given library but not source file,
and appears to not accept paths (which will be needed for pluggables).
Because `gInterpreter->LoadFile("path")` will load either a source file
or library by given "path", and is consistent with `dfi`'s approach to
path handling, this function appears to be the winner (for now).