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
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
call arrays by reference