Parser does not ignore the first CR-LF in a multi-line string

[ghost]

The TOML 1.0.0 spec states about multi-line strings that

A newline immediately following the opening delimiter will be trimmed.

The term "newline" is somewhat ambiguous in this sentence, but the ABNF grammar shows that newline in this context must be taken to mean either LF or CR-LF.

But the tomlkit parser only trims opening LF in a multi-line string, not CR-LF:

import tomlkit
doc = tomlkit.parse('v = """\r\nfoo"""\n')
print(repr(doc["v"]))

prints:

'\r\nfoo'

This suggests that the \r\n combination immediately following the opening quotes has not been trimmed.
If the example TOML document is changed to use only \n instead of \r\n, the tomlkit parser does in fact trim the newline from the string value.

This issue applies to the latest commit 6512eaa on master as well as the latest release v0.11.6.

I'm experimenting with a TOML fuzzer which revealed this issue. I guess most normal applications are not likely to hit this case, so I understand if this gets low priority. It still seems worthwhile to fix it though.