Request for DataFrame.to_tsv() for reading tab delimited text 
I propose a function, which can be called on a DataFrame, named to_tsv or to_table. The function is the equivalent of `to_csv()` with the argument `sep='\t'`. While `to_tsv()` contains the functionality to write tsv files, I find it annoying to always have to specify an additional argument. I prefer tsv files to csv files because tabs more rarely occur and therefore decrease the need for escaping. I also find the plain-text rendering more readable. I worry that the lack of a dedicated `to_tsv()` function encourages the use of csv over tsv. Currently `read_table()` defaults to tab separators, but there is no equivalent function for writing.
