Forest v2.0.0-rc1

v2.0.0-rc1 = v1.1.0rc1
As far as the functionality (.sty files) is concerned, this commit will produce equal results as v1.1.0rc1 published at this (temporary) location: http://spj.ff.uni-lj.si/forest/forest_1.1.0rc1.zip

Major changes:

• Much improved nodewalks.
• Added temporal propagators before packing node and after packing node.
• Implemented looping mechanisms and more conditionals.
• Implemented library support.
• Introduced registers.

Minor changes:

• Added key default preamble.
• Added key split and friends.
• Implemented anchors parent, children, first, last, etc.
• Implemented aggregate functions.
• Implemented sorting of children.
• Implemented handlers .option, .register and .process args.
• Implemented several friends to process keylist and introduced processing orders.
• Added the optional argument (<stages>) to the forest environment and Forest macro.
• Implemented autoforwarding.
• Implemented flexible handling of unknown keys using unknown to.
• Implemented pgfmath functions min_l, max_l, min_s, max_s.
• Implemented augmented assignment operator <keylist>- for removing keys from keylists.
• Implemented a generalized fit to key.
• Implemented (a very slow) forest-based indexing system.
• Added some minor keys: edge path', create' and plain content.
• Added some developer keys: copy command key, typeout.
• In library linguistics: implemented sn edges, nice empty nodes, draw brackets, c-commanded and c-commanders;
• In library edges: implemented forked edges and folder.

Bugfixes:

• In computation of numeric tree-structure info, when called for a
  non-root node.
• Adapted to TikZ's externalization internals.
• delay was not behaving additively.
• Options name, alias and baseline didn't work properly when setting them for a non-current node.
• Augmented assignments for count options were leaking `.0pt'.
• create didn't work properly in some cases.
• triangle (now roof in the linguistics library) didn't use cycle in the edge path.