Rachel format nuclear data files

Rachel accepts the standard Gosia data 

* Excited states' lifetimes
* Measured matrix elements (signed)
* Measured branching ratios (not including internal conversion branches)
* Measured E2/M1 mixing ratios  

in addition to the measured relative gamma-ray yield data in the file <tt>rachel_nuclear_data.txt</tt>, which must be in the working directory in order for Rachel to find it.

The Rachel file format differs from the standard Gosia input for these data and is "human readable":

<pre>
branching initial_band initial_spin final_band_1 final_spin_1 final_band_2 final_spin_2 branching_ratio error
mixing    initial_band initial_spin final_band final_spin mixing_ratio error
lifetime band spin lifetime[ps] error[ps]
< final_band final_spin || multipolarity || initial_band initial_spin > = signed_matrix_element error
...</pre>

where "branching," "mixing," "lifetime" and the bra and ket notation are fixed formatting symbols and ''band'' is a valid text band name in Rachel.  The "<", ">" and "||" symbols should be delimited by spaces.  Note the "upward" direction for the matrix element (from lower- to higher-numbered state) and the standard units of the appropriate powers of e, b and nuclear magnetons.  The individual entries can be given in any order, for example in the file <tt>rachel_nuclear_data.txt.EXAMPLE</tt>, which comes with the Rachel distribution:

<pre>
# This is a test file.  Data are meaningless!
lifetime gsb  2.0  400. 80.                          # in picoseconds
<  gsb 2.0 || E2 || gsb 0.0 > = 2.17 0.02            # Sign is interpreted as positive [eb]
mixing gam 2.0 gsb 2.0     0.35 0.05                 # any user comment
< gamod 3.0  || E2 || gsb 4.0 > = -0.45 0.12         # Sign is interpreted as negative
< gsb 2.0 || E2 || gamod 3.0 >  =  0.23 0.08         # BACKWARD--WILL BE TIME-REVERSED!
# Note that time-reversal is done automatically for a consistent phase convention.
branching gam 8.0 gamod 7.0 gsb 6.0 0.042 0.005      # gamma decay branches only--not including conversion
#branching band3 3.5 band1 1.5 band1 2.5 0.04 0.01   # This line is commented out
lifetime gam 2.0   5.  2.                            # cite Jane Doe, PRC 5, 289 (1994)
</pre>

The order of the individual lines is completely arbitrary.  The file is re-read each time Gosia is called, so individual lines can be "commented out" before a Gosia fit iteration.  Note that the sixth line contains a matrix element given in the ''decay direction'', whereas Gosia requires it to be in the ''excitation direction''--from lower-numbered state to higher-numbered state.  This phase of this matrix element will be automatically time-reversed before being included in the fit data.  ''Pay special attention to the mixing ratios, which are the amplitude ratios with a phase as defined in Krane and Steffen, PRC 2:724.  These are not intensity ratios which may be found in some catalogs.  Refer to the Gosia manual section on OP,YIEL for units.''

The weights given to each of these four data sets can be set via the ''Gosia controls'' button menu, for example to test whether there are systematic conflicts between the different data sets (and/or the gamma-ray yield data).