Base64 Encoding/Decoding

[dkinzer]

These routines can be used to encode a series of bytes using the Base64 alphabet and then decode back to the original data.

Note: the test code in this module uses a style of Program Memory data item initialization that was added after the release of v0.42.0 of the compiler. Until you have a version that supports quoted string data initialization you'll have to modify the test data.