CLN: create io.api for io relegated read_xxx
related to #3418

should auto generate class methods for the io
and delay the imports until actually called

(including html, excel, csv, hdf, dta)

deprecate these  methods as well:
https://mail.google.com/mail/u/0/?shva=1#inbox/13ec1cd9b60c5bda

at the very least should deprecate:

```
from_csv -> pd.read_csv
from_dta -> pd.read_dta
```
