Logging: replace required Commons Logging with optional SLF4J, falling back to Java Util logging

This patch was inspired by @spmiller's work on a pluggable logging interface.  This patch caters to
two main audiences: those two don't want any extraneous dependencies (by removing the need for
commons logging) and those who want to be able to redirect and/or suppress logging via standard
logging configuration (when SLF4J and a binding are provided).

https://github.com/marceloverdijk/lesscss-java/pull/16
Update README.md to reflect that commons logging is no longer required, and SLF4J may be used
Add a constructor to LessSource to be able to specify encoding
Merge pull request #27 from trecloux/source_encoding

Add a constructor to LessSource to be able to specify encoding
Merge pull request #25 from davidmc24/optional-slf4j

Logging: replace required Commons Logging with optional SLF4J (fallback to java util logging)
[Fix] import failed when closing brace is on same line
Remove File dependency from LessSource. Introduce abstract Resource.
Add more javadoc to Resource.java
Update README.md
Make lesscss java compiler compatible with 1.4 less import directive
Merge pull request #35 from Jahia/master

Make lesscss java compiler compatible with 1.4 less import directive
Merge branch 'master' of https://github.com/apechinsky/lesscss-java into apechinsky-master

Conflicts:
	src/main/java/org/lesscss/LessSource.java
Merge branch 'master' of https://github.com/4ntoin3/lesscss-java into 4ntoin3-master

Conflicts:
	src/main/java/org/lesscss/LessSource.java
support for lesscss 1.4.1
Merge branch 'master' of git://github.com/marceloverdijk/lesscss-java

Conflicts:
	pom.xml
	src/main/java/org/lesscss/LessCompiler.java
	src/main/java/org/lesscss/LessSource.java
	src/main/resources/META-INF/less.js
	src/test/java/org/lesscss/LessSourceTest.java