Sed awk grep removal

[themadprofessor]

Replace calls to sed, awk, grep, etc with the regex crate where possible.
Currently, don't have access to a machine with Wi-Fi, so those calls have been left in for now.

Closes #725

[themadprofessor]

That's the remaining calls replaced.
The regexs for iwctl and nmctl haven't been tested as I don't have a machine with those commands, but they should work.
If someone can test those, that would be great.

[ammgws]

The fallback logic is broken. I only have iwctl installed and I get:

Error in block 'net': Failed to execute SSID query using iw.

However the previous behaviour was that it didn't fail on iw and instead fell back to the next possible command until it reached iwctl.

[themadprofessor]

Whoops, good spot. Should be fixed now.

[ammgws]

Hmm, current master and the below config works fine but pulling in this branch causes it to fail. It shouldn't fail since bitrate isn't specified in the config. I'm sure the bug itself is unrelated to this PR though.

[[block]]
block = "net"
format = "{ssid}"

>./target/debug/i3status-rs test.toml
{"version": 1, "click_events": true}
[[{"background":"#000000","color":"#dc322f","full_text":" Error in block 'net': Failed to execute bitrate query with iw. ","separator":false,"separator_block_width":0}]

Error in block 'net': Failed to execute bitrate query with iw.

[ammgws]

OK I see what's going on. Before it would run, for example, `sh -c "ethtool ... | awk ..." and due to the command being piped to awk/sed/etc the exit code was 0 even if ethtool itself was not installed/failed to run. Now that all those pipes to sed/awk are gone and the command is called directly it is failing as it should have done before.