Creating hyperSpec object without wavelengths

[cbeleites]

This is the "transpose" of issue #288: creating a hyperSpec object where the spectra do not (yet) exist.

Suggested:

new("hyperSpec", data = data.frame(c = 1:5))

this works:

new("hyperSpec",
     wavelength = numeric(0),
     spc = matrix(NA_real_, ncol = 0, nrow = 5), 
     data = data.frame(c = 1:5)
)

[GegznaV]

I've solved this on my PC, just did not want to create too many PR before the current ones are reviewed.

[GegznaV]

To clarify, I have suggestion for:

new("hyperSpec", data = data.frame(c = 1:5))

[GegznaV]

I ran unit tests on my implementation and understood that the issue is more complex than it seemed at first glance.

Currently, the official solution to this issue in hyperSpec is to use as.hyperSpec():

as.hyperSpec(data.frame(c = 1:5))

as.hyperSpec(as.matrix(data.frame(c = 1:5)))

as.hyperSpec(matrix(1:5))

[GegznaV]

Issue reopened as r-hyperspec/hyperSpec#99