Update and rename readme.md to README.md

Added some information about what you get out of this demo in terms of UDO's
HMAC sample program

RFC-2104 compliant HMAC program in BASIC
Updated readme to use Markdown syntax

Updated readme to use Markdown syntax and also clarified requirements around UniData/UniVerse versions
Merged Jing's updated comments
Corrected license information

Also removed authorship and date information as this can be tracked via commit details.