Updating API docs with feedback

- (some of) the nomenclature changes for method names, codes/arguments
- typo removal
api: nomenclature changes!

- createVariable to createColumn
- getVariable to getColumn
- setVariable to setColumn
- add_arg to add_code
- change_arg to change_code
- also changes names of files, their paths, and references thereto
api: openSHAPA -> datavyu -- needs verification