error in the tests, did not update the blank properties, and add to one

See merge request bbatardiere/pyplnmodels!27

simulate the data to take as parameters pln_param, a new class
containing all the parameters (components, coef, offsets and covariates.).

_init_S in _utils.

test other fixtures.

compile the docs. updates some RuntimeError to ValueError.

renaming PLNPCA to PlnPCAcollection and _PLNPCA to PlnPCA. Now PlnPCA is

See merge request !26

it.

public. PlnPCAcollection is a collection, I implement all the required
methods such as __getitem__ etc, and wrote tests for it.

updated tests for the from_formula init and removed setup.py to get a

See merge request !20