String to Integer (atoi)

Implement myAtoi(s), which converts a string to a 32-bit signed integer. Follow these steps:

1. Skip leading spaces (only the space character).
2. If the next character is + or -, read it as the sign. Without a sign the number is positive.
3. Read digits until a non-digit or the end of the string. Ignore everything after.
4. If no digits were read, the result is 0.
5. If the value is outside the 32-bit signed range [-2^31, 2^31 - 1], clamp it to the nearest bound.