command: split filter changing in two functions

One function sets a raw filter list, the other allows "editing" the
filter list.
command: add vf/af properties
command: make vf and af commands more verbose

On success, print the filter chain on the OSD. Otherwise, show an error
message on the OSD (just enough so that the user knows whether the
command worked).
option: fix inverted --mouseinput option

Also fixes --no-mouseinput.
demux_lavf: fix API usage

avio_alloc_context() is documented to require an av_malloc'ed buffer. It
appears libavformat can even reallocate the buffer while it is probing,
so passing a static buffer can in theory lead to crashes.

I couldn't reproduce such a crash, but apparently it happened to
mplayer-svn. This commit follows the mplayer fix in svn commit r36397.
demux_lavf: make avio buffer configurable

Perhaps not very useful, but reserved for situations when a user reports
awful latency and experimentation/debugging might be required to find
out why or to fix it (happens often).
core: change speed option/property to double

The --speed option and the speed property used float. Change them to
double.

Change the commands that manipulate the property (speed_mult/add) to
double as well. Since the cycle command shares code with the add
command, we change that as well.

The reason for this change is that this allows better control over
speed, such as stepping by semitones. Using floats is also just plain
unnecessary.
Merge remote-tracking branch 'origin/master' into lua_experiment