Made vis into a package and divided plots between maps and vtk. Fixed recipes to work with new package

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rename : fatiando/vis.py => fatiando/vis/map.py
Todo: fix broken links in vis.vtk
Inplemented basin2d.trapezoidal with option to estimate both x and z coordinates. Doesnt work. gradient methods dont converge. Estimating only z works.
Changed basin2d.trapezoidal to only find the z coordinates. x coords are taken from the other 2 vertices. Made recipe and passes doctests
Quickfix to talwani bug: add 0.1m to coordinates if they are zero or the same. Appears to work well.
Added utils functions to convert between seconds and years
Added heat package for geothermics. heat.climatesignal for direct and inverse. abrupt climate change working with doctests and recipe.
Typo in fatiando.heat docstring
Typo in climatesignal
Added linear climatesignal with direct and inversion + doctest + recipe. Also made recipe using abrupt data and inverting with linear model
Direct modeling of seismic vertical profile passing doctest.
Finished vertical seismic profile inversion + doctest + recipe (needs better plotting)
Plotting of layers in vis.map

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rename : cookbook/recipes/seismic_profile.py => cookbook/recipes/seismic_profile_vertical.py
rename : cookbook/recipes/srtomo.py => cookbook/recipes/seismic_srtomo.py
rename : cookbook/recipes/srtomo_sparse.py => cookbook/recipes/seismic_srtomo_sparse.py
Added function for mean and stddev of a list of arrays in utils.
Docstring examples for new utils functions
Finished smoothness regularizer 1D. Fix to Damping: taking norm of p when should be norm of p squared
Finished smoothness 2D. Missing sparse smoothness. Fixed damping doctest

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rename : cookbook/recipes/seismic_srtomo.py => cookbook/recipes/srtomo_damped.py
rename : cookbook/recipes/seismic_srtomo.py => cookbook/recipes/srtomo_smooth.py
Removed legacy reg module. Added square2polygon function in mesher.dd so that can use talwani nicely with a square mesh
Replace _makefd methods in smooth with calls to fdmatrix*d functions so that can reuse them in total variation without multiple inheritance
Added TotalVaritation with 1D class. Implemented it in vertical seismic profile. Results are the same as smooth

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rename : cookbook/recipes/seismic_profile_vertical.py => cookbook/recipes/seismic_profile_vertical_sharp.py