Seek to byte after `#DATA` in Perkin Elmer IR (PEIR) format

[davidbenncsiro]

Should seek to byte after #DATA in Perkin Elmer IR (PEIR) format since the preceding text length may differ per file!

Need a format spec!

[davidbenncsiro]

https://github.com/csiro/soilspec.format/blob/main/R/perkin_elmer_format.R#L229

[davidbenncsiro]

Use grepRaw.

[davidbenncsiro]

Allow for possibility that the string to see after is: #DATA\n or #DATA\r\n