add comment arg to read_table

[cboettig]

tokenizer_fwf already has an option for comment, but for some reason this seems to have been omitted from read_table, though it is present in all other read_ methods (and in read.table()). Adding it back here.

[hadley]

This will also need to be fed in to fwf_empty()

[jimhester]

Thanks! The repo this PR comes from seems to have gone off into the nether, but I re-created your commit manually (d65b23d) with Hadley's suggestion.

[cboettig]

@jimhester apologies, it looks like my commit didn't actually fix the issue so I removed it. That change allows read_table to take a comment arg, but it is effectively ignored and so the function still chokes trying to parse commented white-space delimited tables. I guess that is why it was omitted in the first place, looks like something will have to be changed lower down to skip comment symbols on read_table.

Here's a reproducible example (from a classic data set):

read_table("ftp://aftp.cmdl.noaa.gov/products/trends/co2/co2_mm_mlo.txt", 
                  comment = "#)

[jimhester]

As of 7ab8634 this show now work properly

library(readr)
read_table("ftp://aftp.cmdl.noaa.gov/products/trends/co2/co2_mm_mlo.txt",
  comment = "#", col_names = FALSE)
#> cols(
#>   X1 = col_integer(),
#>   X2 = col_integer(),
#>   X3 = col_double(),
#>   X4 = col_double(),
#>   X5 = col_double(),
#>   X6 = col_double(),
#>   X7 = col_integer()
#> )
#> # A tibble: 706 × 7
#>       X1    X2       X3     X4     X5     X6    X7
#>    <int> <int>    <dbl>  <dbl>  <dbl>  <dbl> <int>
#> 1   1958     3 1958.208 315.71 315.71 314.62    -1
#> 2   1958     4 1958.292 317.45 317.45 315.29    -1
#> 3   1958     5 1958.375 317.50 317.50 314.71    -1
#> 4   1958     6 1958.458 -99.99 317.10 314.85    -1
#> 5   1958     7 1958.542 315.86 315.86 314.98    -1
#> 6   1958     8 1958.625 314.93 314.93 315.94    -1
#> 7   1958     9 1958.708 313.20 313.20 315.91    -1
#> 8   1958    10 1958.792 -99.99 312.66 315.61    -1
#> 9   1958    11 1958.875 313.33 313.33 315.31    -1
#> 10  1958    12 1958.958 314.67 314.67 315.61    -1
#> # ... with 696 more rows