This continues the work begun by #1585. It moves each info manual's
directory metadata to the top of the file, where it needs to be.
I couldn't see a way to do this with pandoc/makeinfo, so the Shake
recipe prepends it from a separate file.
With this metadata in place, the hledger info manuals can be added to
an Info dir file using install-info. Eg:
$ install-info hledger/hledger.info /usr/local/share/info/dir
$ info
Secondly, the Shake "manuals"/"infomanuals" recipes now also generate
an Info dir file in each package directory, so you can also just add
the package directories to your INFOPATH. Eg:
$ export INFOPATH=~/src/hledger/hledger:~/src/hledger/hledger-ui:~/src/hledger/hledger-web:$INFOPATH
$ info
