Support {% ifchanged Expression(s) %} like Django does

Django ifchanged can accept parameters, so it is possible to check for a value
which does not appear in output. Django documentation says to support one or
more parameters, this implementation supports up to 4 paramters (only limited
by the parser expression, this can be improved to support even more
parameters when needed).

{% for date in list %}
  {% ifchanged date.month %}
     {{ date.month }}:{{ date.day }}
  {% else %}
     {{ date.day }}
  {% endifchanged %}
{% endfor %}

See erlydtl_unittests for some other examples.

The other (Django) syntax to use {% ifchanged %} without parameter works like before.
Merge pull request #24 from thge/master

Extended {%ifchanged %} syntax to accept parameters
Merge pull request #26 from fauxsoup/master

Use lists module for erlydtl_runtime:find_value
Support arbitrary number of arguments to ifchanged
Fixed date formatting for 'h', added tests.

Removed extra integer_to_list conversion from tag_to_value/3 for $h.
Added tests for "h", "H", "i", and "Y" to each test case.
Merge pull request #30 from bluegraybox/master

date 'h' format fix
More flexible "_" function
Extend the regroup syntax to support nested keys

This commit allows the user to use nested regroup keys. ie.

    {% regroup builds by host.name as hostname_list %}
Make dictsort use deep find
Add testcases for nested regroup and dictsort
Merge pull request #27 from garazdawi/regroup_extend

Allow nested keys in regroup and dictsort
Add unit tests for {% elif Expr %} syntax
Add support for {% elif Expr %} syntax
Merge pull request #35 from psyeugenic/egil/support-elif

Support {% elif %} clause in if template tag syntax
Added postgresql timestamp output format test.
Added handling floating point seconds in time tuples.
Use integer_to_list_zerofill instead of regular integer_to_list.
Refactored and fixed a bug when seconds (float or integer) < 10.
Updated datetime 4 test to reflect last logic change.
Merge pull request #36 from runejuhl/fix-pgsql-timestamp

Fix pgsql timestamp