Liblet

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- Bumped ANTLR jar to version 4.8.
- Fixed a few typos in docs (thanks also to andreazube)

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- Bumped the major version, non new features expected since this year class is done.
- Added the parameter fail_on_error to the liblet.antlr.ANTLR.context method to make
it return None in case of parsing errors
- Modified the liblet.antlr.ANTLR.tree method so that it returns None in case of
parse errors
- The liblet.antlr.ANTLR.tree method does not include nodes for the EOF token.

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- The liblet.display.Tree.with_threads method puts nodes at the same rank according to
their depth in the tree.
- The liblet.antlr.ANTLR.tree method ignores <EOF> tokens for non simple trees.

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- Added new documentation for recently added classes and a few utils.
- Moved the liblet.display.warn method to liblet.utils.warn.
- Fixing the None node display style in liblet.display.Tree.with_threads.

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- Added HTML escaping to liblet.dislpay.iter2table and liblet.dislpay.dict2table.
- Added liblet.display.Tree.with_thread method.
- Added liblet.antlr.AnnotatedTreeWalker class.

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- Added and fixed ANTLR class tests.