Span.end: Fix definition to match comment.  Now is index after last
token of span; (was index of last token of span).  Fixed internal usages
for new definition.  WARNING:  If you use Span.end (including
TokenSpan.end) directly, you should fix your code.
Span.value: Now immutable; (was mutable, tracking future changes to
the Span).
Merge branch 'master' of git@github.com:factorie/factorie.git
Changing Spans so that they don't automatically add themselves to a ChainWithSpansVar.
new spans: fixing type issue
new spans: removing This type, which is no longer necessary in Span and SpanVar, and drastically simplifies what the code looks like
Merge pull request #1 from alextp/newspans

Fixing the type issue with the new spans
Now that TokeSpans are not automatically added to the Document, 
make Mention be a TokenSpan, not contain a TokenSpan
(as recently discussed with Alex).
Phrase, NounPhrase, etc: Proposed as a replacement for Mention.
Then re-create Mention specific for coref.
Merge pull request #54 from andrewmccallum/newspans

Simplified version of Spans that are not automatically added to a list.  Mention is now a Span.  New app.nlp.phrase.