Reflection profiles: Fundamental parameters approach

[vincefn]

Add Fundamental parameters approach for reflection profiles. Would be a lot of work, probably long computation times. Relevant litterature/code:

• J. Appl. Cryst. (1998). 31, 851-861 https://doi.org/10.1107/S0021889898006876
• J Res Natl Inst Stand Technol. 2004 Feb 1;109(1):1-25. https://dx.doi.org/10.6028/jres.002
• J Res Natl Inst Stand Technol. 2015; 120: 223–251 https://dx.doi.org/10.6028%2Fjres.120.014
• http://dx.doi.org/10.6028/jres.120.014.c [Python code for 2015 FPAPC article]