Bump go to 1.19 and go mod tidy

Upgrade mvdan/sh

Merge pull request #12 from bouk/wordhdoc

Translate word Hdoc <<< expression

Merge pull request #10 from bouk/quote-more-words

Quote the word values in unset substitutions

Update test to reflect changes

Implement recursive sourcing

Use string collect -N

Update README with new command subst

Add README

Add README