feat(headers): return hyper::Error instead of () from header components

[pyfisch]

This allows more precise errors in the future and makes it easier to use
the try!() macro in some cases.

BREAKING CHANGE: Error enum extended. Return type of header/shared/
types changed.

[seanmonstar]

typo ivalid

[coveralls]

Coverage increased (+0.03%) to 85.45% when pulling 3acc852 on pyfisch:errors into c8086db on hyperium:master.

[seanmonstar]

I don't get why you want to use Error::Value here, instead of Error::Header. A Value could be from just about anything, no?

[pyfisch]

Ok, I will suse Error::Header but I think it is a bad thing to reuse a header code. Error::Header is already used by httpparse. The relativly precise Errors from the parser are merged into a few codes, I think this is bad because you loose useful information, but this is not the topic here.

[coveralls]

Coverage increased (+0.03%) to 85.64% when pulling 5d66939 on pyfisch:errors into ca6cf2b on hyperium:master.

[coveralls]

Coverage increased (+0.03%) to 85.64% when pulling 5d66939 on pyfisch:errors into ca6cf2b on hyperium:master.

[seanmonstar]

Optionally, a specific header could have it's own error types. Such as if there are multiple specific things that can go wrong during parsing it...

[coveralls]

Coverage increased (+0.03%) to 85.64% when pulling 5d66939 on pyfisch:errors into ca6cf2b on hyperium:master.

[pyfisch]

Yes it could habve one. Any problems remaining?