A bunch of little changes that together enable external image support.
Try:
```
tiddlywiki editions/tw5.com --verbose --build externalimages
```
Then open `externalimages.html`, look for the images in the more/types
tab of the sidebar, open them and verify that they are set with an
external SRC attribute, not a data URI.
We’re also reverting to the old custom dropdown. Using the select
widget didn’t work out because it couldn’t cleanly work with a text box
allowing custom types to be specified.
1. Moved some methods out of boot.js because they are not needed until
after bootup
2. Added alternate message for editing an overridden shadow tiddler
3. Minor style tweaks
By rearranging the `[all[]]` operator we are able to ensure that shadow
tiddlers get processed before ordinary tiddlers. This makes it easier
to create custom stylesheets that override the core.
We get a significant speed improvement of >10% by rearranging filter
operators to bring to the front the operators likely to reduce the size
working list.
Fixes#82.
The old behaviour was to parse the content of a widget or html element
in block mode if the opening tag was followed by a line break. The new
behaviour requires two line breaks.
This makes it possible to include linebreaks more liberally within
wikitext, although care must still be taken to only use double line
breaks when the block mode behaviour is desired.
The code change here is very simple, just a single line change in
html.js. Most of the other changes are to convert various single line
breaks into double line breaks.
