Removed arguments from Tiddler.update()

The arguments includeInternal and includeMacros were supposed to allow
the caller to select which links should be included. In practice, none
of the callers pass any arguments, so the defaults are always used.

There was a bug in handling wiki-style links inside <<choice>> macros:
the "m" match object was used, which was set in an earlier loop,
instead of the "item" match object that contains the <<choice>> match.
This didn't lead to any visible problems because the regular link
finder would also find all wiki-style links inside macros.

Since it would require extra effort to ensure that when includeInternal
is False the update() method wouldn't pick up wiki-style links inside
macros, I decided it was better to instead drop the includeInternal and
includeMacros arguments.

I did an additional cleanup in parsing the old style <<choice>>
argument syntax: it would strip off text before the pipe character,
but that is relevant only in wiki syntax.
Further simplification of Tiddler.update()

Don't bother to assign the expression iterated through to a variable
when it is only used by the following "for" statement.

Add to the "actions" list using extend() instead of list concatenation.
This avoids creation of a new list object.
Collect links in a set in Tiddler.update()

Previously, the links were collected in several lists, then combined,
converted to a set (to remove duplicates) and then converted back to
a list. That involved a lot of unnecessary work.
Also deduplicate image references in Tiddler.update()

The links were deduplicated, but the images were not. I don't see any
reason for this difference.
Merge pull request #110 from mthuurne/tiddler_update_simplify

Tiddler.update() simplification