core: Allow arbitrarily large config values
core: Upgrade config schema on install to allow arbitrarily long config values
mod_bootstrap: add bootstrap 3.0.0 along side v2.3.2.

Include `bootstrap-3/...` to get the new version.
Fixes #640. Migrating other modules/sites to bootstrap 3 is another issue.
authors: added Channel.me and David Halls.
mod_bootstrap: fix image path.
doc: mod_mqtt documentation. Fixes #642
doc: fix table.
docs: add doc about MQTT JavaScript lastwill.
core: Refactored z_lib_include to use the dispatcher when creating lib urls.
docs: minor table fix in mqtt docs.
docs: mod_qmtt, clearify the javascript message buffer and Qos
doc: fix MQTT doc header levels.
doc: minor changes for mqtt docs.
mod_base: minor: tidy up in controller_postback.
mod_base: add template action.

This makes it easier to send template data as response to postback and submit events.

Without template action::

   {Output, Context1} = z_template:render_to_iolist("response.tpl", z_context:get_all(Context), Context),
   z_context:add_script_page(Output, Context),
   Context.

With template action::

   z_render:wire({template, [{template, "_license_data.tpl"}|z_context:get_all(Context)]}, Context).

It also avoids a round-trip to the page session, by keeping the information in the context at all times.
mod_ssl: Return a secure absolute url when it is requested from a secure context.
mod_base: Fix for error which happens when setting up a ws times out.
core: check type of value column in config table before upgrading.
Merge branch 'hanikesn-increase-size-of-config-values'

Fixes #638.
core: Read site config also from files in site config.d.

Site config options are now derived from the files (in order, where options may be overridden by a later file):

priv/config => site/<sitename>/config => site/<sitename>/config.d/*

Where files from the config.d directory is read in alphabetical order, ignoring those beginning with . or ending with ~.
These files are usually backup or other irrelevant files.

Fixes #648.