read in EML numHeaderLines and pass into read_d1_files

[atn38]

Hi! Great work on the package. I'm trying it out ahead of this year's EDI Hackathon where we'll develop a tool to auto generate visualizations from data+metadata. This is such a great first step.

I'm testing on this VCR-LTER package which turns out to be a great test case. EML doc specifies 17 columns and read_d1_files returns two because of extra header lines. But EML doc does say how many there are -- 22, so that information should ideally be made use of.

There's the ... option to pass in an argument (from #16). It'd be neat though if the numHeaderLines EML tag can be passed into skip if default function read_csv is used. Alternatively (additionally?) read_d1_files can throw a warning if it doesn't find the number of columns expected in EML docs and suggest probable cause (extra head rows) so users know to pass an extra parameter.