Now that MSVC support for C99 is quite good, remove previously needed but
now unused checks and definitions, like PRI* format macros (including
PRIdMAX and TR_PRIuSIZE, replaced with %jd and %zu) and inline macro.
Also, remove ssize_t typedef and replace few occurences with ev_ssize_t.
Also, remove check for stdbool.h availability (guaranteed by C99) and
include it unconditionally (except when in C++ mode).
1. add the option the code to be used under GPLv2 or GPLv3; previously only GPLv2 was allowed
2. add the "proxy option" as described in GPLv3 so we can add future licenses without having to bulk-edit everything again :)
3. remove the awkward "exception for MIT code in Mac client" clause; it was unnecessary and confusing.
