Less verbose cli errors

[jeremyfowers]

Closes #76 by printing only usage and a hint, instead of the full help page, on CLI arg errors.

Demos

(tkml) jefowers@XSJ-JEFOWERS-L1:~/turnkeyml/models/selftest$ turnkey cache stats --blah

error: the following arguments are required: build_name

Run 'turnkey cache stats --help' for more information

usage: turnkey cache stats [-h] [-d CACHE_DIR] build_name

(tkml) jefowers@XSJ-JEFOWERS-L1:~/turnkeyml/models/selftest$ turnkey cache blah

error: argument cache_cmd: invalid choice: 'blah' (choose from 'report', 'list', 'stats', 'delete', 'clean', 'location')

Run 'turnkey cache --help' for more information

usage: turnkey cache [-h] {report,list,stats,delete,clean,location} ...

(tkml) jefowers@XSJ-JEFOWERS-L1:~/turnkeyml/models/selftest$ turnkey golboddy  report

error: argument COMMAND: invalid choice: 'golboddy' (choose from 'benchmark', 'cache', 'models', 'version')

Run 'turnkey --help' for more information

usage: turnkey [-h] COMMAND ...

(tkml) jefowers@XSJ-JEFOWERS-L1:~/turnkeyml/models/selftest$ turnkey bob.po

error: input_files must end with .py, .onnx, or .txt (got 'bob.po')

Run 'turnkey benchmark --help' for more information

usage: turnkey benchmark [-h] [-a] [-b] [--labels [LABELS [LABELS ...]]]
                         [--script-args SCRIPT_ARGS] [--max-depth MAX_DEPTH]
                         [--device {nvidia,x86}]
                         [--runtime {ort,trt,torch-eager,torch-compiled}]
                         [-d CACHE_DIR] [--lean-cache]
                         [--sequence {optimize-fp16,optimize-fp32,onnx-fp32}]
                         [--rebuild {if_needed,always,never}]
                         [--onnx-opset ONNX_OPSET] [--iterations ITERATIONS]
                         [--rt-args [RT_ARGS [RT_ARGS ...]]]
                         [--use-slurm | --process-isolation]
                         [--timeout TIMEOUT]
                         input_files [input_files ...]

[danielholanda]

Excellent. Thanks!