fixes #1010

safe / sequential replacing of formatstrings for date conversions

please review & test
fr-FR translation for three introductory tiddlers on Filters.
add Japanese Translations
Merge pull request #1229 from tobibeer/fix-1010

fixes #1010 sequential date formatstrings
Some tests and style updates for #1229

@tobibeer I simplified the handling of matched strings a little.
Add heeg.ru to resources
Merge pull request #1230 from pekopeko1/japanese5.1.6

add Japanese Translations
Merge pull request #1233 from xcazin/fred2

fr-FR translation of three introductory tiddlers on Filters