Sasmodels

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* Doc update: Archive built docs on Github
* Doc update: Display math correctly
* Fix parameter name checking in kernel call

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* Doc upate: corefunc and optimizer documentation
* Doc update: various models (cylinder, gel_fit, paracrystal, core_shell_ellipsoid)
* Fix error in BCC and FCC paracrystaline models
* Fix rare race condition causing errors
* Fix to allow multiple scattering scripts to run
* Fix problem with models containing complex amplitudes not compiling on the fly
* Restructuring and cross-linking of sasmodels docs
* Update web links and contributor list

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* implements generalized 3D description of magnetic SANS
* adds Boucher-type SLD profile to the selection in the model spherical_sld
* improves naming conventions of constants in magnetic SANS
* composite mixture models with multiplicity are now allowed
* improvements to the superball model
* fix to bug in magnetic SLD calculations
* updates to documentation

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* fix probelm with P(Q) scaling when using a shell type form factors
* fix problem with wide Gaussian approximation to resolution function at
very low Q which could sometimes extend into negative Q by truncating the
resolution contribution at Q = zero
* added support for complex math using openCL
* a number of doc updates

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* doc update: how to test a plugin model in 5.x version

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* fix polydispersity for python models
* fix dll cache so multiple versions can coexist
* fix caching bug on pyopencl for Intel on OS/X
* fix tinycc compilation bug on windows indicating bad backslash escape
* warn if ER function is present in plugin model but not used
* restore python 2.7 support