Bumps

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* add --view option to command line which gets propagated to the model plotter
* add support for probability p(x) for vector x using VectorPDF(f,x0)
* rename DirectPDF to DirectProblem, and allow it to run in GUI
* data reader supports multi-part files, with parts separated by blank lines
* add gaussian mixture and laplace examples
* bug fix: plots were failing if model name contains a '.'
* miscellaneous code cleanup

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* gui: undo code cleaning operation which broke the user interface

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* population initializers allow indefinite bounds
* use single precision criterion for levenberg-marquardt and bfgs
* implement simple, faster, less accurate Hessian & Jacobian
* compute uncertainty estimate from Jacobian if problem is sum of squares
* gui: fit selection window acts like a dialog

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* accept model.par output from a different model
* show residuals with curve fit output
* only show correlations for selected variables
* show tics on correlations if small number
* improve handling of uncertainty estimate from curvature
* tweak dream algorithm -- maybe improve the acceptance ratio?
* allow model to set visible variables in output
* improve handling of arbitrary probability density functions
* simplify loading of pymc models
* update to numdifftools 0.9.14
* bug fix: improved handling of ill-conditioned fits
* bug fix: avoid copying mcmc chain during run
* bug fix: more robust handling of --time limit
* bug fix: support newer versions of matplotlib and numpy
* miscellaneous tweaks and fixes

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* add entropy calculator (still unreliable for high dimensional problems)
* adjust scaling of likelihood (the green line) to match histogram area
* use --samples to specify the number of samples from the distribution
* mark this and future releases with a DOI at zenodo.org

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* tweak uncertainty calculations so they don't fail on bad models