Update and rename readme.txt to README.md

Converted file from .txt to markdown format.
Update .gitignore

Added .DS_Store to .gitignore
Delete .DS_Store

.DS_Store is not necessary
Merged all Readme files into one
Delete readme-ubuntu.txt
Delete readme-mac.txt
Merge pull request #33 from caffinatedmonkey/master

Merge READMEs and convert to markdown format