Make the ISM reader accept both Windows- and Linux-style line endings
When using ISM metadata files with both CR LF line endings, the reader will end with an error (invalid metadata value provided). This is caused by the is_number function that correctly ignores LF characters, but not CRs, try e.g. attached file. Changing this to accept other line-endings as well requires a minimal fix only, adds convenience and removes a source of confusion, especially because error reporting is not ideal yet.