[New] `nvm use`/`nvm install`: add `--save` option #1305

Job	Run time
shellcheck_matrix (bash, nvm.sh)	57s
shellcheck_matrix (sh, nvm.sh)	45s
shellcheck_matrix (dash, nvm.sh)	43s
shellcheck_matrix (ksh, nvm.sh)	39s
shellcheck_matrix (bash, install.sh)	23s
shellcheck_matrix (bash, bash_completion)	29s
shellcheck_matrix (bash, nvm-exec)	30s
shellcheck	1s
	4m 27s

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