Rearranged the project to mag it go get-able.

The project is rearranged to make it get along with go get.
It can now be installed with:
'go get -tags [openmpi/mpich2] github.com/JohannWeging/go-mpi'
Removed cgo config go files.
Updated readme to go get.

On branch go-getable
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

    modified:   README.md