Adds Task interface for getting data
Adds Contact interface for getting data
Merge branch 'contacts' into dev

Conflicts:
	harvest/api_client.go
	run_examples.go
Adds ExpenseCategory interface for reading data
Explicit returns and use anonymous field
Code cleanup, simplification

* Removes modules.go in favor of keeping small struct in only file that
  references it
* All returns explicit
* [Some] shortened variable names
* Single imported packages on one line
* Moves non-standard library package imports after standard library
  imports
* More embedded/anonymous fields, which necessitates changed return
  types
* Adding default empty values for return where an error precludes
  generating the actual return value
Reverse return value order so error is last

This is more intuitive and in keeping with Go conventions