Rename sys.update and sys.failsafe: add _policy_path
Add hello world tutorial
Merge pull request #151 from tzz/tzz/feature-sys-variables2

Rename sys.update and sys.failsafe: add _policy_path
Volker learns the alphabet
Modify hello world tutorial for Nick.
Add `keywords` tag.

Allows registering of keywords that register as targets for
auto links from `keyword`.
Remove some hand-coded links, rely on autolinks.
Document reverse()
Document containers, readjson(), and parsejson().  Note the two alternative merging syntaxes.
These are recognized and linked to automatically
Non longer needed with smarter syntax-map generation.
Document new macros and include some examples.
Generate promise attirbute docs from syntax map.
Include example source from... example source.
Merge pull request #163 from tzz/feature/json

Document containers, readjson(), and parsejson().  Note the two alternative merging syntaxes.
Fix links, some editing.
Include initial section on containers (needs more work)

Restructure and edit a bit, take out "Datatypes" header.
Document `clist` as a possible type in promise attributes.
Publish the rrange function docs.

The function is documented as "not used anywhere", but by not publishing
it we end up with dead links or incorrect warnings about undocumented
syntax.
Some editing and add a TODO for documenting special usage
of functions of type boolean.