Rachel format nuclear data files

Rachel accepts the standard Gosia data (in addition to the measured relative gamma-ray yield data) in the file rachel_nuclear_data.txt.  The file format is as follows.

<pre>
branching initial_band_name initial_spin final_band_name_1 final_spin_1 final_band_name_2 final_spin_2 branching_ratio error
mixing    initial_band_name initial_spin final_band_name final_spin mixing_ratio error
lifetime band_name spin lifetime[ps] error[ps]
<final_band_name final_spin || multipolarity || initial_band_name initial_spin> = signed_matrix_element error
...</pre>

Note the "upward" direction for the matrix element (from lower- to higher-numbered state) for the matrix data and the standard units of the appropriate powers of e, b and nuclear magnetons, for example

<pre>
lifetime band1 2.5 27. 3.                    # in picoseconds
<band1 4.5 || E2 || band1 2.5> = 2.54 0.38   # Sign is interpreted as positive.
mixing band1 2.5 band1 1.5 0.35 0.05         # any user comment
<band5 5.5 || E3 || band1 2.5> = -0.23 0.12  # Sign is interpreted as negative.
branching band2 2.5 band1 2.5 band1 1.5 0.100 0.020  # gamma decay branches only--not including conversion
lifetime band1 3.5 5.  2.                    # cite Jane Doe, PRC 5, 289 (1994)
</pre>

The order of the individual lines is completely arbitrary.  For example, see the example file [[File:Rachelnucleardata.txt]], which should be renamed as above so that rachel.py will find it in the working directory.