Code cleanup

No logical changes.
Removing unnecessary commenting.
Renaming variable names to use snake-case naming.
Change MajorType and AdditionalType bit masks to be binary constants instead of hex
Renamed AdditionalType simple enums to be prefixed with SIMPLE instead of INT
Restructured encoder switch statement and added encode functions for each data type

Also added a STRING_ENCODING constant to Cbor class which determines how
strings are converted before being CBOR encoded. UTF-8 is CBOR standard.
Created a function which abstracts encoding a major type and it's data length/value

This function uses mostly the same code as the original encodeInteger
function. The encodeInteger function now calls this one.
Added unit tests for encoding booleans, nulls, and unknown types
Added some basic unit tests for encoding strings