added regression test for useless SS segment override (#9)

Merge branch 'regress_x86_address' of https://github.com/mrexodia/beta into mrexodia-regress_x86_address

propagate the error of missing symbol back to ks_asm(). this adds new error code KS_ERR_ASM_SYMBOL_NOTFOUND. fix issue #61

add error code KS_ERR_ASM_SYMBOL_REDEFINED to report redefined symbols. also updated all the bindings after this

Support nasm USE32 and GLOBAL directives.

Make directives case-insensitive.

Both nasm and gnu assembler use case insensitive directives.

Added tests for intel/nasm label artithmetic