plasma_atomic_compare_exchange_*

plasma_atomic_compare_exchange_*
plasma_atomic_compare_exchange_n_*
plasma_atomic_exchange_n_*
minor: move plasma_atomic_{load,store}* to C11 sec

minor: move plasma_atomic_{load,store}* to section with C11 interfaces
minor: rename 'order'->'memmodel' for consistency
atomic load/store seq_cst w/o two full mem syncs
add C11 memory model to plasma_atomic_fetch_*
minor: doc
rename LICENSE -> CREDITS
use clang and GCC __atomic_fetch_* when available
plasma_atomic_fetch_*_explicit() for 32 and 64-bit
xlC asm for 64-bit ldarx/stdcx. in 32-bit program

xlC asm for 64-bit ldarx/stdcx. in 32-bit program on 64-bit hardware