started separating binary tiddler contents from metadata

this makes storage more efficient when the metadata is modified

plus Base64-encoding binary contents seems generally inefficient
fixed use of quotes for consistency
ensured binary files are committed

do note the comment on how metadata files are considered the
authoritative source

in the process, expanded existing test for robustness
added test for binary contents

image source:
http://publicphoto.org/technology/floppy-disk-1-44-mb/attachment/floppy-disk-1-44-mb_fujifilm-mf2hd_23010/
improved efficiency and readability

only slightly, but seems worth it - even though it's kinda weird relying
on a variable declared in another if branch
ensured binary files are removed on deletion
ensured tiddler and revision listings correctly handle binaries
renamed binaries directory to avoid title conflicts

using _ instead of . as prefix to avoid conflicts with locking mechanism
changed conflict exception

as suggested by @cdent