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.
Added UDO Demos directory README file
Moved HMAC into a 'Security' category.

Moved HMAC into the 'Security-Demos' directory  to keep examples
organized by category.
Consistent structure

Mainly to make example structure consistent and to make it easier to
expand the structure for more complex examples.
Merge pull request #5 from dmcgrath/master

Updated readme's and structure changes (HMAC - Security)