[MRG] DOC A few fixes in the docstrings of all classifiers.

- [x] Make the multiple lines in docstring appear without any extra spaces in between the two words where multilines are separated by `\` at the end of 1st line.

**docstring**
Before : 
```
    coef_ : array, shape = [1, n_features] if n_classes == 2 else [n_classes,            n_features]
```

After : 
```
    coef_ : array, shape = [1, n_features] if n_classes == 2 else [n_classes, n_features]
```
**html**
No change

- [x] Refactor a few multiline imports to make them look neater.

A very minor PR, @jnothman could you take a look...
More broadly, we need to merge our numpydoc back into the numpydoc project, and add fixes there...