Add README

A must for good Github repos
Add Contribution Guidelines

Github will "add a link to your file when a contributor creates
an Issue or opens a Pull Request".
https://github.com/blog/1184-contributing-guidelines
Made unix domain sockets work on Linux.
Made the fix apply to all unices and added a unit test.
Mark std.string.chop and its unittest as @safe and pure
Mark leftJustify, rightJustify and center as pure
Merge pull request #1512 from tom-tan/safe-pure-string-chop

Mark std.string.chop and its unittest as @safe and pure
Merge pull request #1454 from qznc/readme

Add README and CONTRIBUTING files
Merge pull request #1496 from jerro/unix-domain-sockets

Fixed std.socket.UnixAddress
Merge pull request #1513 from tom-tan/pure-string-justify

Mark leftJustify, rightJustify and center as pure