global variables present when reading data

[bvreede]

The following note is given when checking the package.

These globals are OK, because the input file has a particular architecture that includes specific names. That said, it would be nice to write this in a more robust manner.

* checking R code for possible problems ... NOTE
clean_content: no visible binding for global variable ‘Parameter’
clean_content: no visible binding for global variable ‘type’
extract_header: no visible binding for global variable ‘X1’
extract_header: no visible binding for global variable ‘level_1’
extract_header: no visible binding for global variable ‘level_2’
extract_header: no visible binding for global variable ‘Value’
Undefined global functions or variables:
  Parameter Value X1 level_1 level_2 type

Same as #10 :)