Make the parsing metadata more flexible

[atao60]

This request answers to the three enhancements suggested by Make the parsing metadata more flexible(intelligent) #180:

• Allow blank lines in header of content files
• Allow spaces around equal of a header entry
• Allow multi-lines value for header entry value

About this last point: any line starting with 2 spaces will be concatenated with the previous line.

[jonbullock]

Thanks for the contribution.

[jonbullock]

I've been reviewing this PR and I've come to conclusion that I won't be taking the change in. The reason being I don't want to complicate the structure of the metadata header, it's simple as is and while this fixes #180 I don't agree with part of the original change to allow multi line options. The structure of the header is clearly set out, one line = one option. Having said that, the other two suggestions I see as making the parsing code more tolerant which can be addressed with a couple of small code changes.

Thanks again for taking the time to contribute and apologies for the time it's taken in reviewing this PR.