Added some API example, both in code and in README.adoc
Added explanation section on the current work and milestone targets
Linked straight to code in github
Merge pull request #124 from alexsnaps/Doc

Added some API example, both in code and in README.adoc
Fixed relative links to work on github
Got rid of relative links

but for the "forward only pointing" one
draft of Expiration and impl in OnHeapStore