Fix inconsistency: change "--loop-mode" command-line option to "--loopmode"

[M374LX]

If one looks at the command-line options, no one except --loop-mode has a hyphen in the middle: --samplerate, --bitrate, --oversampling, --allowroot.

Thus, for consistency reasons, I suggest changing it to --loopmode.

There is another detail: the output of --help lists --output-format as an option, but it is actually --format.

[Wallacoloo]

I'm pretty neutral as to the hyphen vs non-hyphen discrepancy, so I'll just see what others have to say.

Another thing is that the help for the bitrate option says:

-b, --bitrate <bitrate>     specify output bitrate in kHz
                            default: 160.

The dimensions there are incorrect. bitrate is bits/[time], whereas Hz is just 1/[time]. My guess is that the intention was for the unit to be kbps (and I'm thinking this only applies to ogg export).

[M374LX]

Another possibility is shortening it further to --loop, as in #2131.

[tresf]

Thanks. Changed to --loop per 2nd suggestion. Also addressed other typos via de40aa8.