corrected description of filterbar_items attribute (item option names in examples)
fixed regex in truncate function

The old version didn't match the h1, h2, ... elements correctly and
caused a wrong </h> closing tag.
some whitespace changes; removed "visible" field, added "hidden" field only where required
added and implemented shortcode attribute "initial_event_id"
some shortcode atts descriptions and whitespace changes
fixed initial_event_id handling
added option to show upcoming events only in the feed

issue #64
preparation for version 0.6.5
small readme fix
Merge branch 'develop'
added option caption for filterbar item reset
fixed line break in option values
added and implemented filter element years option "years_order"

issue #68
css styles modification

issue #67

Testing this modification with some themes didn't cause any problem, so
this change shouldn't have any bad impact.
added already available "past" in initial_date sc option values
structural changes in "get_actual_date" and "get_actual_cat" functions
moved filter_walker to separate function; added filter_walker for the date

This is a preparation to implement date_filter shortcode option (issue
#53)
moved filter syntax description to seperate section in about page

Removed this part from shortcode option description "cat_filter".

This is a prepartation to implement date_filter shortcode option (issue
#53).
small improvements in cat_filter
implemented date_filter

issue #53