CSS Parser Code

Missing impl of com.steadystate.css.dom.CSSUnknownRuleImpl.setCssText(String) added; some more unit tests

fix javadoc link

Possible NPE in com.steadystate.css.dom.CSSImportRuleImpl.getCssText() fixed

Possible NPE in com.steadystate.css.dom.CSSFontFaceRuleImpl.getCssText() fixed

Wrong null handling in com.steadystate.css.dom.CSSCharsetRuleImpl.getCssText() fixed.
getCssText() now returns also the semicolon, because this is part of the rule per spec.
again more unit tests

NPE fix, more unit tests, code cleanup

test method toDebugString() also

testcase added

code simplification

#51 again; If a rule contains the same property twice, the CSSStyleDeclarationImpl methods getPropertyDeclaration, getPropertyValue, getPropertyCSSValue, getPropertyPriority, and setProperty are now returning (or updating) the latter one instead of the first one.