implemented atoi, atol, and strto(u)l(l) in assembly

[ZERICO2005]

Changes:

• Implemented atoi, atol, strtol, strtoul, strtoll, strtoull in assembly.
• Optimized llmulu_b

CC per decimal digit
atoi    :  21F +  4R +  3W +  1
atol    :  32F +  4R +  3W +  1
strtol  :  79F + 13R + 12W + 21
strtoll : 103F + 10R +  9W + 33

atoi, and atol, now have their own dedicated routines which offer a good performance boost compared to wrapping strtol. This is because they don't need to track endptr or overflow, and they only work with base 10.

A dedicated routine for atoll wouldn't be much faster than strtoll since the main bottle neck is multiplication.

I also added __strtoi and __strtoui, which behave exactly like strtol and strtoul, but will raise ERANGE and return INT_MIN/INT_MAX and UINT_MAX respectively when the result is out of range. This is mostly useful for implementing std::string.stoi(), which is supposed to throw an exception if the result is out of range for int. We can't throw exceptions on the eZ80, but using __strtoi allows for ERANGE to be raised instead.