Tangos

* Fixes a bug in the auto-detection of floating/integer numbers within text-based halo stat files (such as those generated by AHF)
* Clarifies the documentation on using Changa's black holes
* Fixes a bug where images would be incorrectly smoothed when using `tangos write` in default load mode
* Reinstates the ability to import simulations from another database (although this feature is currently quite slow)
* Adds ability to store chunked time histograms at a different time resolution for each simulation

* Adds support for using rockstar catalogues for gadget simulations, and importing consistent trees merger information
* Fixes bugs in following merger information when cross-linking information is also present
* Speed improvements, especially to merger tree construction and Halo.earliest, Halo.latest methods
* Adds support for the filesystem layout used by the Caterpillar project
* Other minor bug fixes

This is a first of tangos, intended for pre-release testing