Rename CW to confidence_weighted for #257.
Rename AROW to arow for #257.
Rename NHERD to normal_herd for #257.
Rename PA to passive_aggressive for #257.
Rename PA1 to passive_aggressive_1 for #257.
Rename PA2 to passive_aggressive_2 for #257.
Rename regression::PA to passive_aggressive for #257.
Merge pull request #299 from beam2d/feature/abbreviation

Rename algorithms for naming convention discussed in #257