Added LICENSE and copyright to couchbase.
btree imports

import references changed from couchbaselabs account to prataprc account
bug fix.

import github.com/prataprc/btree changed to,
import github.com/prataprc/gobtree
moved tools/fsck.go to tools/fsck/
Created individual sub-dirs for each main package.
type conversion in tests/insert_sbench.go program.
TODO updated.