This function converts a null-terminated ASCII string representing a signed number to a signed int value.
The string should be in one of the following forms:
Table 1. Input strings
| "-0b10000000" to "0b11111111" | binary |
| "-0o200" to "0o377" | octal |
| "-0200" to "0377" | octal |
| "-128" to "255" | decimal |
| "-0x80" to "0xFF" | hexadecimal |