Extend getValue to support slices and sections

[jdlrobson]

currently running <<view field text>> allows the view macro to access the field with name "field" on the current tiddler.

It seems logical that <<view ##field text>> would print the section with name "field" and likewise <<view ::field text>> would print the slice with name field.

This becomes extremely useful when making use of the templating supported by the list macro on tiddlers with slice/sections. (See  https://groups.google.com/group/tiddlywiki/browse_thread/thread/b29b12d52932b5e6)

It can be achieved by improving the getValue function. Patch and tests (previously not existent) attached.

[MartinBudden]

Fixed in changeset:12743