Use only awk when getting window information

- use bash builtins to control the while loop
Exit normally after showing usage
Merge branch 'master' of https://github.com/jnvsor/screencap into awk
Replace backticks with $()
Use break when exiting the loop
Drop $u_capture and $u_scale
Use array sizes to assign map_{a,v}, assign filter_v earlier

- must use quotes when adding audio inputs
- now if $blind is used, $filter_v is not used
Replace some arrays with variables
Revert "Replace some arrays with variables"

- ffmpeg sees each of the array's items as a one big argument

This reverts commit 159fb1b24b25e131ab760c6b64f5fea26b948c87.
Revert "Use array sizes to assign map_{a,v}, assign filter_v earlier"

- ffmpeg sees each of the array's items as a one big argument

This reverts commit e6d34b56eab3824048c848a6e259c8a95909a20e.
Assign filter_v earlier so that $blind can unset it
Merge branch 'test' into framerate