gnucash-htdocs master: Add the pdf, epub, and mobi links for old docs 2.6.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash-htdocs/commit/bc714449 (commit)
	from  https://github.com/Gnucash/gnucash-htdocs/commit/203f6a2c (commit)



commit bc71444922408187e1a3f972ea5212c0e05a237b
Author: John Ralls <jralls at ceridwen.us>
Date:   Sun Jun 28 13:28:12 2020 -0700

    Add the pdf, epub, and mobi links for old docs 2.6.



Summary of changes:
 docs.phtml | 112 +++++++++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 76 insertions(+), 36 deletions(-)