Add changelog for v0.3.2 (#125)

Add changelog for v0.3.1 (#111)Add changelog for Choclo v0.3.1.

Add changelog for v0.3.0 (#104)Add changelog for Choclo v0.3.0. Include link to new docs in`versions.rst`.

Add changelog for v0.2.0 (#81)Add changelog to documentation. Add link to the docs for Choclo v0.2.0in `doc/versions.py`

Add changelog for v0.1.0 (#55)Add changelog and link to the docs for the new version. Force usinghttps for links to previous documentation pages.

Add magnetic fields of prisms (#17)Add forward modelling functions for the magnetic field of a single rectangularprism on a single computation point. These are three functions for eachcomponent of the magnetic field vector and one other `magnetic_field` functionthat computes all three in a more optimal way. Make these functions to reusethe kernel functions defined for the gravity forward modelling. Add symmetrytests for the new functions, test if the magnetic field has zero divergance andif the `magnetic_field` function generates the same output as the three otherfunctions. Rename `prism/_forward.py` to `prism/_gravity.py` and`test_prism.py` to `test_prism_gravity.py`.