New help text layout option and hook for generating custom help text

[Xunnamius]

Two things:

1. Implement showHelpOnFail.layout with two options: 'default', which is the current behavior (yargs::showHelp), and 'single-column', which emulates typescript's help text layout (npx tsc --help).

2. Implement configureHelpTextLayout hook, which receives context (including meta and programs for each command) and the help text that would have been output with respect to showHelpOnFail.layout, and returns a string that will be output to the terminal as the help text.

TypeScript's (tsc) single-column help text looks really nice, and makes optimal use of the available terminal width. Eventually, I'd like to use it for my own CLI projects.

Time horizon is unbounded on this one, though.