IO IRAF fixes

A few small fixes:

* for one example I tried to load, the 1d wavelength array had shape [4096,1] but the flux had shape [4096], so I added a `squeeze()` in `wave_1dspec`
* changed capitalization of `read_IRAF_spec`
* added `__inits__`
* use `Spectrum1d.from_array` instead of `__init__`

Let me know if you like these changes; I want to start using your IRAF reader.