[Feature request] add parameter to redirect temporarily path

[lsylsy2]

Scenario:
When capturing videos using a server (VPS, Cloud server, etc.), it's usual to have system disk and data disks seperated, and /tmp mouted to the system disk which is not big enough to hold all the segment files.
Adding a parameter allowing to save temp files in specified path can solve this problem.

[Last-Order]

You can use environment variables (TEMP on Windows or TMPDIR on common Linux distributions) to set the directory of temprorary files.

On Windows:

set TEMP=D:/temp/&& minyami ...

On Linux

export TMPDIR=/foo/bar && minyami ...

[Last-Order]

Docs updated.