wrapper functions to generate stock assessment inputs

[sgaichas]

• combine functions for survey index, survey catch at age, survey length and weight at age

• combine functions for survey catch data

[sgaichas]

now have functions to

• om_init initialize the operating model with a config file

• om_species selecting out a single species or subset of species

• om_index creating survey and fishery indices using a config file

• om_comps creating survey and fishery age and length comps using config files

Still in progress

• wrapper to write SS3 dat file

See here for development notes

[sgaichas]

wrappers index and comps have been updated to allow for multiple surveys and have been tested for multispecies datasets

added wrapper om_diet for multispecies diet data

still could use wrapper functions to write inputs for multiple assessment models