Add COLOR and KEY to *MPI-NAMING-CONVENTIONS*
Add COLOR and KEY to *MPI-NAMING-CONVENTIONS*

Prior to this change, the build failed, like so:

    ; file: /home/quicklisp/quicklisp-controller/dist/build-cache/cl-mpi/ab72e2e330571a02451fa733bd7f55c325634dc6/cl-mpi-20190701-git/mpi/contexts.lisp
    ; in: DEFMPIFUN "MPI_Comm_split"
    ;     (MPI::DEFMPIFUN "MPI_Comm_split"
    ;                     (MPI::COMM MPI::COLOR MPI::KEY MPI::*NEWCOMM))
    ; --> MPI::SINCE-MPI-VERSION PROGN
    ; ==>
    ;   (CFFI:DEFCFUN ("MPI_Comm_split" MPI::%MPI-COMM-SPLIT)
    ;       MPI::MPI-ERROR-CODE
    ;     (MPI::COMM MPI:MPI-COMM)
    ;     (MPI::COLOR NIL)
    ;     (MPI::KEY NIL)
    ;     (MPI::*NEWCOMM (:POINTER MPI:MPI-COMM)))
    ;
    ; caught ERROR:
    ;   (during macroexpansion of (DEFCFUN ("MPI_Comm_split" %MPI-COMM-SPLIT) ...))
    ;   The value of SYMBOL is NIL, which is not of type (AND SYMBOL (NOT NULL)).
    Unhandled UIOP/LISP-BUILD:COMPILE-FILE-ERROR in thread
    ; #<SB-THREAD:THREAD "main thread" RUNNING {10005E05B3}>:
    ; COMPILE-FILE-ERROR while compiling #<CL-SOURCE-FILE "cl-mpi" "mpi"
    ; "contexts">

See also:

https://github.com/marcoheisig/cl-mpi/pull/25#issuecomment-507307193
https://github.com/marcoheisig/cl-mpi/pull/20

marcoheisig/cl-mpi,marcoheisig/cl-mpi