Added liquid templating and migrated first agents
Use liquid in the matches section of EventFormattingAgent
LiquidMigrator is checking for complex JSONPaths

If a complex JSONPath like '$.text[*]' is found the migration will
fail with an exception and keep the database intact
Migrated the PushbulletAgent to use LiquidInterpolatable
Migrated JabberAgent to use liquid, added link to documentation
Migrated DataOutputAgent to use liquid
Migrated TranslationAgent to liquid
Migrated TwitterPublishAgent to use liquid
Made migration irreversable, support '$variable' syntax
Add JiraAgent

The agent does periodical queries and emits
the events containing the updated issues in JSON format.

The agent also supports HTTP basic authentication.
Migrated HumanTask, Trigger and PeakDetectorAgent to Liquid

Made LiquidInterpolatable#interpolate_options recursive
Really interpolate the `message` options attribute of the PeakDetectorAgent
Merged all previous liquid migrations into one new migration
Added support for the `Agent#make_message` format to the liquid migrator
Merge remote-tracking branch 'huginn/master' into liquid-templating
Removed unused code
Fix date/time manipulations in jira_agent.rb

During testing, I figured out that jira doesn't understand
timezones in JQL. Because of this I have to introduce a
workaround that fetches issues 24 h earlier that the requested
date and then filters out unnecessary ones based on the
value of 'updated' field.
Addressed review comments by @cantino
fix typo in jira_agent.rb
introduce request guards in jira agent
rename MAX_REQUESTS to MAX_EMPTY_REQUESTS in jira agent
make JiraAgent more testable and fix some minor issues detected during testing
add RSpec tests for JiraAgent