Log event filtering added. Filters not yet initialized. Not tested

Filters allow log events to be evaluated to determine whether they
should be published. Filters are typically useful to implement more
complex filtering rules than a filter on the logger's name and/or
on the event level. A typical example would be the use of a regular
expression to filter out messages of a certain kind.

Filters may apply context-wide, within loggers or within appenders.
For more info, see:
http://logging.apache.org/log4j/2.x/manual/filters.html

Woodman does not support appender reference filters for the time
being.

Filters still need to be created by LoggerContext during
initialization.

Code is most likely not operational in any case as it has not been
tested yet.
Updated RegexFilter to accept events by default upon match

Accepting events by default is more in line with the way regular
filter functions work. This behavior can be overridden when the
filter is created.
No fake context-wide filter created by default

The LoggerContext created a fake accept-all context-wide filter but
that's no longer needed.
Filters created during initialization. Ready for testing

Filters referenced in the configuration are created when Woodman is
initialized. The configuration may reference context-wide filters,
logger filters or appender filters. Each configuration may either be
an array or an object indexed by the filter's type.

Example of a context-wide filter using an array:
  {
    "filters": [
      {
        "type": "RegexFilter",
        "regex": "Hello"
      }
    ],
    "appenders": [...],
    "loggers": [...]
  }

Same example with an object:
  {
    "filters": {
      "RegexFilter": {
        "regex": "Hello"
      }
    },
    "appenders": [...],
    "loggers": [...]
  }

Code is ready for testing but has not been tested yet.
Unit tests added for RegexFilter and CompositeFilter classes
Unit tests added on filters initialization, code fixed accordingly
RegexFilter added to all Woodman distributions
Unit tests added on filtering. Code fixed accordingly

The unit tests cover simple use cases of a context-wide filter, a
logger filter and an appender filter. Code in Logger.js fixed, the
Message instance was created after trying to apply filters, making
filtering crash.
v0.2.0

Changelog since v0.1.9:
- Feature: String parameters substitution support: log('H{}!', 'ey');
- Feature: Decision to use "toString" based on method overloading
- Feature: PatternLayout supports non abbreviated conversion patterns
- Feature: Log event filtering supported, RegexFilter created
- Chore: switched to require.js shortcut notation
- Bug fix: JSONLayout did not return the right object structure