Small changes
Moved server.go from indexing/server/main/ to indexing/progs
Moved server app to progs/

Added TODO items.
Updated TODO list.
Added Compare() method to `Key` interface.

Correspondingly types implementing `Key` interface under keys.go implements
Compare() method-receiver.
Example REST URI and corresponding methods.
Changed NInf and PInf to NegInf and PosInf.