Implement function to pull new bcadata

[matdehaven]

This will be the main function of the package.

It pulls all of the data from sources online.

• [x] Function to pull FRED data (takes FRED key)
• [x] Function to pull TFP data (if possible)
• [x] Function to make the right transformations to the series
• [x] Function that combines the above, returns new bcadata

[matdehaven]

Completed, ended up writing one function for last two tasks.