NO-JIRA: README improvements

[dnwe]

• remove out-of-date product information from the README and include the more
  current information from the website
• add a new INSTALL file to contain the build and install instructions
  from the existing README
• move all development and testing related info from that to the
  DEVELOPERS file
• better explain how to run the various test suites and how they work
  across proton-c and proton-j in the developers file
• other misc improvements across the contents of the files
• rename DEVELOPERS and INSTALL to have .md suffixes for better
  rendering on GitHub
• add a symlink from README --> README.md for better landing page
  rendering on GitHub

[rhs]

+1

As a general note I think it's good to try to test changes to install/readme type stuff on people who aren't already intimately familiar with proton and all its various quirks. I wouldn't hold up merging this for that though.

Nice work, BTW! It's great to see this sort of stuff get cleaned up!

[dnwe]

I've sent these off to be further reviewed by a few people round here to see if I can determine further improvements., Have merged them in as-is for now as I believe they're a decent first pass at improving what we currently had.

@mcpierce fyi, this will require an update to the rpm qpid-proton.spec to account for the new file extension of README.md

[asfbot]

Abhay Saxena on proton@qpid.apache.org replies:
Make install tries to install README instead of README.md.