Tests: switched to RequireJS shortcut notation. BaseURL defined.

The shortcut notation is now used consistently across Woodman.

Setting RequireJS "baseURL" in the test runner is actually a good
idea because RequireJS does not know how to normalize paths that
go above the folder that contains the test runner by default and,
while it correctly resolves modules in the end, it fills the modules
array with names such as:
 spec/../../lib/./loglevel
 spec/../../lib/././loglevel

... which has the annoying drawback that module variables that should
typically be defined once and for all are actually defined once per
entry in the modules array.

Setting the baseUrl to the root folder solves the problem.
Make "registerLevel" create matching functions on Loggers (#16)

Log levels are not defined as a singleton array anymore. Each
LoggerContext now references one instance of a LogLevel object,
passed around to Logger and Appender so that they can call tell
when a trace level is below another one.

Distributions typically call "registerStandardLevels" or
"registerLevel" to set the levels that they handle.

Logger instances now expose trace functions whose name match that
of the registered log levels, making levels a flexible and easy-to-use
mechanism. New trace functions are added to existing loggers when the
configuration is loaded (but this will be done as soon as
"registerLevel" is called in a later commit).
"registerLevel" propagates trace functions to existing loggers (#16)

This ensures that new trace functions are available as soon as the
"registerLevel" function returns.