Add function pad-seq

add a function for padding a sequence to a multiple of some value with
supplied padding value.
Finish work on encode

Get base64 encoding working by finishing up all the functions and
problems.
Try to not automatically replace LF with CRLF
rename encode to base64
move bit-ops to common; add decode-base64
Add test for function invert-map
clean up base64 code

add some documentation and make maps private.  Also move pows-of-2 map
into common. Also some formatting in commons, as well as making some
defs private.