Added function documentation

-Modified calculator.lua to have a luadoc style comment for calculator
Finished implementing functionality of calculator

-Changed helper functions to be local functions
-Implemented error checking for bad inputs
Removed excess lunit files
Removed excess lunit files
Revert "Removed excess lunit files"

This reverts commit 01358b3a48480aeb1908824be8a4b657c85b58ce.
Removed error checking because

-I want conflict for you guys
Deleted arbitrary lunit
Updated README, test.lua

-Fixed specifications as depicted in the README
-Added bad input test for test.lua
Updated README, test.lua

-Fixed specifications as depicted in the README
-Added bad input test for test.lua
Fixed bug in test.lua and changed default behavior in calculator

-If the operator does not exist, return error instead of nil
-Fixed bug in test.lua with pcall
Fixed bug in test.lua with call to pcall
This commit merges the 'documentation' branch into 'master'
- edited the calculator.lua file to resolve a conflict
- code from 'documention' branch was kept
- comments from 'master' branch were added

Conflicts:
	calculator.lua
This commit merged the 'documentation' branch into 'master'
- Resolved conflict in calculator.lua file
- replaced function stubs in 'master' with completed functions in 'documentation'

Conflicts:
	calculator.lua
This commit removes unnecessary lines from calculator.lua
- the last merge added unnecessary lines such as >>>>>>HEAD
- these lines interfered with program compiling
- these lines were removed