Analysis stages

[l-gorman]

Creating draft PR as I work on breaking down calculations into the three main analysis. This is what I am working on:

• Break down into three analysis stages #
• Add TLU conversions to list of tables to be verified by users Issues in livestock_tlu_calculations() #32
• Add extra conversions for other livestock and rename ducks Issues in livestock_tlu_calculations() #32
• Deal with HDDS issue HDDS duplicate columns #16
• Generalise the identification of repeat loops Checking for repeat Loops #19
• Fix list definitions how to handle list definitions #21, load unit and conversions into an object rather than into the global environment
• Add option to investigate other uses (e.g feed livestock) and fix case where there is a single use, and a proportion. Fixes proportions_calculation() function - add 'process' option #37
• Add runnable examples
• Add number of hungry months Nr of Months Food Insecure #8