Add a check for -lpthread.
Create Release and Debug directories if they are not present.

Otherwise, build fails if these directories do not exist.
Added .gitignore
Add automake-generated files to .gitignore
Convert README and INSTALL instructions to markdown.
Rename README and INSTALL files to give them a .md extension.

So that they are recognized as markdown and displayed correctly on the web.
Fix markdown title and pandoc-style metadata.