Support for skip_rows_after_header option in reading csv files

[JonGretar]

Adds support for the skip_rows_after_header option.

This is helpful when dealing with generated CSV from scientific instruments that may have metadata after the header row.

For example when we look at this CSV file:

"TOA5","6843","CR3000","6843","CR3000.Std.22","CPU:CA_Flux__GOOD.CR3","24006","ts_Above"
"TIMESTAMP","RECORD","Ux","Uy","Uz","co2","h2o","Ts","press","diag_csat"
"TS","RN","m/s","m/s","m/s","mg/m^3","g/m^3","C","kPa","m/s"
"","","Smp","Smp","Smp","Smp","Smp","Smp","Smp","Smp"
"2012-06-07 13:00:00.05",111868400,0.468,-0.9077501,0.1785,659.7584,9.530561,28.52527,100.1938,0
"2012-06-07 13:00:00.1",111868401,0.60275,-1.0795,0.283,660.0234,9.492132,28.51141,100.1938,0
....

In this case we want the second row as the header and would use the following call:

Explorer.DataFrame.from_csv!(csv_path, skip_rows: 1, skip_rows_after_header: 2)

Closes #781