Store debugging logs

[d3m3vilurr]

New configure options save_debug_log

If enable this flag, currently, save connection logs to ux0:data/moonlight/moonlight.log
But sadly, we still cannot detect detail error information of moonlight-common-c like RTSP handshake.
This project use stderr for the logging & always return same error code(-1)
so sometimes we need to modify this project.

Anyway this hacky print method will help debugging for user's specific problem at next times.

[cgutman]

Moonlight-common-c does need some updates to improve error codes, but I don't think you'll get much useful data from RTSP handshake that isn't already there. RTSP error -1 almost always means that the ENet connection timed out, which is usually some firewall issue or incompatible software on the PC.

[d3m3vilurr]

this pr is just to add debug printing to file, it make to help debugging like #42 case. :)

btw, in my case, sometimes want to detail information of the moonlight-common-c.
actually my case was this(yea... probably most reasons are this case)
vita version cannot print any debug console message, also message about just got rtsp handshake error make hard understand to enduser (they will think what is rtsp? :) )

i guess, if we can get these debug messages(``Failed to connect to UDP port 48010, RTSP OPTIONS request failed`, ...), more helpful for the end user.

Limelog is more complicate in this case.
this macro looks like designed platform independent & capsulation, and many cases just print to stderr.
but we cannot see debug console on the working, so we only can use alternative methods(like psp2shell, file, whatever) and initialization of their methods require module outside, sometime passing values to the module inside.
i think, it make to break design, so i mentioned just result error codes :)