Data Type: BIGNUMERIC support

[eduardodrc]

There is a new decimal type BIGNUMERIC available for Big Query tables (see data types docs). When we load a table with this type, we receive the error message:

Running job 'example' [\]  1s
Complete
Billed: XX.XX MB
Downloading Y rows in Z pages.
Error in bq_parse_files(schema_path, page_paths, n = page_info$n_rows,  :                              
  Unknown type BIGNUMERIC

I think that we can just map BIGNUMERIC to float type (Rcpp::DoubleVector), but I'm not a master here. A similar request in the python SDK can help python-bigquery/ issue 367.

Thank you for the great work!

[hadley]

I'd very much appreciate it if anyone could make me a reprex for this issue, i.e. some code that created a table with a BIGNUMERIC field and then tried to download from it. That would save me a little time and allow me to fix the underlying problem a little bit faster.

[hadley]

I think the easiest thing to do (which I'll do for all unknown types) is to just return the string data, so you can do what you will with it.