feat: use a pager for all large terminal output, not just for help

[simonmichael]

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This is an impactful change, and I value the CLI and easy scriptability. But it has been working well for help output, and I for one am ready for it. Feedback, testing and problem reports welcome.

Doc:

Paging

On unix-like systems, when displaying large output in the terminal, hledger tries to use a pager when appropriate: the one specified by the PAGER environment variable, otherwise less if available, otherwise more if available. The pager shows one page of text at a time, and lets you scroll around to see more. While it is active, usually SPACE shows the next page, q quits, and ? shows more features.

The pager is expected to display ANSI color and text styling if possible. hledger adds R to the LESS and MORE environment variables to enable this in less (and in its more compatibility mode). If you use a different pager, you might need to configure it similarly, to avoid seeing junk on screen. Or you can set the NO_COLOR environment variable described below.