softcut buffer fixes

[catfact]

fixed a couple lua/OSC commands:

/softcut/buffer/clear : this was broken in SoftCutClient
/softcut/buffer/clear_region_channel : this was broken in matron/weaver

added:

• /softcut/buffer/write_mono [sffi]; args: path, start (seconds), dur (seconds), channel (zero-based)

• /softcut/buffer/write_stereo [sff]; args: path, start (seconds), dur (seconds)

for all the buffer functions, dur=-1 means to read/write/clear the entire buffer. (or, read the entire file if that is shorter.) (there is an attempt in OscInterface.cpp to provide defaults for missing arguments, but it turns out liblo doesn't work this way and the handlers aren't called at all. so this should be cleaned up too.)

have not yet added lua/weaver glue for write commands, nor tested on norns HW (only on desktop crone with raw OSC.)

(happy to add glue and test sometime next week, unless someone else can get to it first.)

also:

• both read and write are unnecessarily slow (1 frame at a time.)
• it might be good to have crone send some OSC back to matron when these operations finish.

[catfact]

oh, NB: as with Tape, output format is 24-bit fixed, 48k, wav. format is arbitrary; chose 24b instead of float as a compromise for the limited disk space on norns.

[tehn]

aha dur=-1 awesome, thank you! and file writing, wow. i can add the glue.