Nestly

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* Fix bug wherein pop does not work on nest levels added with a function (GH-23).

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* Add support for automatic alias creation in ``SConsWrap`` instances (GH-17).

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* Add ``SConsWrap.add_target_with_env`` (GH-14)
* Completely revamped aggregation functionality (GH-15)
* Add ``SConsWrap.add_controls`` (GH-16)

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* Add ``SIG{INT,TERM,USR1}`` handling to nestrun (GH-9)
* Add SCons integration via ``nestly.scons`` (GH-12)
* Support for walking a directory in nestagg (GH-13)
* Initial Python 3, PyPy support
* Add an ``OUTDIR`` key to nest control files
* Additional examples

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* Add ``nestly.core.stripext``
* New aggregation functionality: ``nestagg`` subcommand; ``nestly.core.nest_map``
* Show tail of log file when ``nestrun`` fails (GH-10)

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* Deprecated ``nestly.nestly``
* New object-oriented API in ``nestly.core``
* Updated examples