Release 0.2.1

Added some preliminary features of 0.3, documentation, fixes and quality o life updates:

Changes & Additions:

• Added some more documentations, e.g. added io.rst.
• Converted scale to floats everywhere it is set by default.
• Changed default behaviour of create_vector_homog:
  • 3D Fields now always has 3 components (if theta is not set explicitely, the arrows are oriented in the xy-plane).
  • 2D Fields have only 2 components by default (theta=None), but gain a third component if theta is specified.
• Added comp_pos argument to from_signal method, that can be used to specify which axis holds the components. Also usable by load_field function! Useful for backwards compatibilty with Pyramid.
• vectors.py: More documentations and more fine control over vector and skyrmion chirality and orientation. Closes #47 (closed)!.
• colors: Added a namespace for colormaps (instead of a dictionary) to ease access to the maps. CMAP_CIRCULAR_DEFAULT is therefore deprecated now!
• plot2d: significantly simplified the symmetric color map handling with DivergingNorm (which was built for exactly that).

Fixes:

• Fixed vector default and name saving in ovf.py.
• Fixed vector default and necessity of dim in tec.py.
• Fixed erronous dim -> scale assignment in vtk.py.
• Fixed interp_to_regular_grid not using the multidim. scale correctly.
• Fixed create_vector_singularity function.
• Removed superfluous enumeration in reader/writer in io_field.
• Various smaller bug-Fixes in io.