update `var_comp` to tidy `.gcl` objects

[krshedd]

var_comp still uses old-style, 4-part list .gcl objects

[awbarclay]

I can update this one. The only thing this function needs .gcl objects for is to create a hierfstat file. I have a function that creates a hireftat data object in R that can take the place of reading in a file and it's already updated for the tibble .gcl objects GCLr::create_hierfstat_data(). Do you want the option to read in a hierfstat file or just call on GCLr::create_hierfstat_data() to create the object needed for computing variance components?

[krshedd]

Let's include an option to read in a FSTAT .dat file, but have the default behavior be to use GCLr::create_hierfstat_data(). Does that work for you?

[awbarclay]

That works for me!

[awbarclay]

This function has been updated to use tidy .gcl objects. Other updates: runs in parallel, creates it's own hierfstat data object or reads in and converts FSTAT .dat file, returns a tibble