ccan: add test for line-wrapping usage message.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
opt: accept newline in help strings

This correctly continues on the next line indented.

Signed-off-by: Luke Dashjr <luke-jr+git@utopios.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
opt: test the new embedded-\n-in-usage behaviour.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
opt: don't wordwrap when description line starts with whitespace.

This was suggested by Luke, though his version insisted on using tab.
This one is a bit more complex, but allows either tab or space.

Suggested-by: Luke Dashjr <luke-jr+git@utopios.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>