Don't return EOF as it equals -1 on glibc (and maybe others)

-1 is already used as a return value when an error occurs.
Instead, return 0 when an EOF occurs (0 == nothing has been read),
and 1 when a new section or a key/value pair has been found.
Rename two API functions before it's too late

Rename ini_open_section to ini_next_section
Rename ini_read_key_value to ini_read_pair
Add Python bindings
Added an example program that uses libini to parse a config file