Fix typo

Makefile target for shared library build

Fixed 2 issues in s_header_{field,value} states

If the buffer ended with the '\r' char on the s_header_value state, the parser triggered the on_header_value() callback twice (buffer="data\r"): 1st time with "data" and 2nd time "data\r" resulting in "datadata\r" instead of "data".

If the buffer ended with the '-' char on the s_header_field state, the parser forgot to call the on_header_field() callback due to the wrong 'break'.
Fixed by letting the 'is_last' check to handle the "last-char" situations.

Added some brief examples to the main readme.

Fix incorrect condition of the while loop in multipart_parser_execute

Fix incorrect data size calculation (causing truncation)

Fix issue where CR/LF line breaks would be repeated in the data output

Rearrange things a bit to clean up the code

Change multipart_parser_execute return type to size_t, and save another malloc

Now compiles as ANSI C

init_multipart_parser

Parser can return wrong length for data that spans multiple chunks