Add spectra module

The initial tools are:

- rvcorr: correct for radial velocity,
- line_position: Obtain the poition of the line center,
- subselect_spectra:Subselect the observed array to fit [min_wl,
max_wl]
Add get_fwhm

This function possibilWith this function, the user can obtain the
fwhm of a spectral line.
Remove set_synplot_path. It is unecessary.

To set the path to Synplot, one has only to:

idltools.SYNPLOT_PATH = new_path

There is no nedd of function to that.
Ignore log files
Add statement to import get_fwhm