ENH: Allow passing a list of regular expressions to the usecols keyword argument in read_csv
I'm dealing with some csv files which have hundreds of labeled columns. The first row in the files is the header row. I'd love to be able to load in only specific columns. The 'usecols' keyword argument to `read_csv` is useful but I currently have to read the first line of the file manually to get the header, parse the header into a list of strings, and then identify which column headers match a set of regular expressions to get the index of the header. These indexes can then be passed to 'usecol' so that I don't load those columns. So my feature request is to allow one to pass in a list of regular expressions to 'usecol' as an option to the indices. I'd be happy to contribute this code if you all think it is useful and could point me to the best place to implement it in the source tree.
