The loops that need to be unroll jammed are marked in the clast by setting
    `clast_for->unroll` field to CLAST_UNROLL_JAM. The marked loop is then
    unroll jammed provided the loop nest is rectangular. The implementation also
    supports multi-loop unroll jam, i.e, for a given statement, multiple loops
    enclosing the statement can be unroll jammed. The routine also supports
    unroll jamming of imperfect nested loops. The routine does not check for
    correctness of unroll jam (permutability of loop nest). It is the
    responsibility of the caller to mark the correct loops for unroll jam.

    Routines added in this commit include
            - clast_unroll_jam which is the library interface routine for
              unroll jamming the AST.
            - Routines to deep copy AST. This aids generation of clean-up code
              after unroll jam.
            - Routines to check rectangularity of the loop nest. Currently, it
              checks whether the iterator of the loop being unroll jammed
              appears in the bounds of inner loops or guards of the statements
              enclosed.

Add unroll and jam support using clast.