Treat the first Sentences of Headers as the first sentence of paragraphs

Currently I assign the Sentence.isStartParagraph value of first sentences of
section headers to true.  But we should have a independent flag such as isHeader.
Reneme Sentence.isStartParagraph to Sentence.isFirstSentence
fix typo in symbol-conf-xx.xml
Merge pull request #109 from johtani/fix-typo-symbol-conf

fix typo in symbol-conf-xx.xml
Change License to Apache 2.0

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Merge pull request #110 from takahi-i/change-license

Change License to Apache 2.0
Merge pull request #108 from takahi-i/fix-begin-space-validator-bug

Fix begin space validator bug #100
Katakana SpellCheck Validator #55
adding KatakanaSpellCheckValidator to SentenceIterator.
separeated testDistance in LevenshteinDistanceTest into each topics.
fixed the indentation.
adding a period and changed the comment setntence.
removed the tailing space.
adding private constructor.
changed the name of the static variable, and introduced public static DEFAULT_ variables and initialized the staic variables by them in static initializer.
Adding period.
removed the tailing space.
adding the comments of the public constant variables.