Drop warning for UserComment type assertion

It's too common to warn about.

Allow invalid encoding in EXIF UserComment field

However, emit a warning in this case.

Limit the byte buffer to 10 MB

Which should be plenty for image metadata.

Add LimitNumTags and LimitTagSize

With some senbible defaults.

This is a safeguard against abnormally large image metadata.

Note that there's already a Timeout option that can be set if you want to have the processing fail if it takes too long.

all: Run modernize -fix ./...

Add testfile for undefined usercomment

See #37

Handle CFAPattern with invalid byte order

Updates #34

Add missing out of bounds check

Closes #34

Fix handling of converted undefined floats

Relates to the fix in 93e6518

See gohugoio/hugo#12793

Return undef for all +inf/-inf/nan float values

See golang/go#59627 and golang/go#59627