This should fix all non-erros, leaving only warnings which
are indeed potential problems.
The following warnings should be safe to ignore:
* Conversions of various offsets from uint64 to
std::streamoff/int64 are safe because such offsets have
been obtained via tellg() and other functions
returning std::streamoff in the first place.
* It also works vice-versa since tellg() should not
return negative offsets with exceptions enabled.
* Conversions from char to unsigned char are also ok.
* Unused diag arguments can be ignored (those might be
useful later).
* Annotate all intended fallthoughs.
* Convert UTF-8 text fields automatically to UTF-16
when version is ID3v2.3 or below
-> so conversion from ID3v2.4 to ID3v2.3 or below
doesn't require manual conversion of possibly
UTF-8 encoded fields
* Don't use magic numbers for ID3v2 encoding byte
* Don't warn about UTF-16 Big Endian with BOM
* So everywhere else can be safely assumed that
text values never have a BOM
* Only exceptions are move constructor and move
assignment where the caller must ensure no BOM
is present