New APIs: cs_disasm_alloc() & cs_disasm_buf()

Currently cs_disasm() API allocate memory for disassembled instructions every time it runs, which is expensive if we need to decode a lot of instructions.

This proposal proposes 2 new API:

• cs_disasm_malloc: pre-allocate buffer for instructions

• cs_disasm_buf: disassemble instructions into pre-allocated buffer provided by cs_disasm_malloc

Prototype:

// pre-allocate memory for @count instructions
cs_err cs_disasm_malloc(csh handle, size_t count, cs_insn **insn);

// disassemble @count instructions using buffer pre-allocated by cs_disasm_malloc()
size_t cs_disasm_buf(csh handle,
                const uint8_t *code, size_t code_size,
                uint64_t address,
                size_t count,
                cs_insn **insn);

Sample code will be like (pseudo)

if (cs_disasm_malloc(h, count, &insns) == CS_ERR_OK) {
    while(c = cs_disasm_buf(h, code, size, address, count, &insns)) {
        // analyze instructions in @insns
        length = CS_INSN_OFFSET(insn, c);
        code += length;
        size += length;
        address += length;
    }
}