Clarify how zero-valued header parsing changed from diactoros 1.x to 2.x

[S1ructure]

Signed-off-by: Florian Hofsaess florian.hofsaess@check24.de

Q	A
Documentation	yes
Bugfix	no
BC Break	no
New Feature	no
RFC	no
QA	no

Description

Since the old implementation didn't add headers with '0' as content there is a significant change in parsing headers. That said the hasHeader will lead to true starting with ^2

Especially when headers are used for handling specific logic it will lead to a significant impact.

I'd say that the old implementation was buggy here. Fixing this bug should be mentioned in documentation to enable users to review their usages of hasHeader and getHeaders activly

[Ocramius]

Overall OK with the changes, but:

1. ::fromGlobals() is the entry point (and should be mentioned)
2. check CI failures :)

[S1ructure]

Overall OK with the changes, but:

1. ::fromGlobals() is the entry point (and should be mentioned)
2. check CI failures :)

done :)

[Ocramius]

Excellent, thanks @S1ructure!