[#2544] Correctly parse Multipart-mixed POST HTTP request in case of entity ends with odd number of 0x0D

Motivation:
When an attribute is ending with an odd number of CR (0x0D), the decoder
add an extra CR in the decoded attribute and should not.

Modifications:
Each time a CR is detected, the next byte was tested to be LF or not. If
not, in a number of places, the CR byte was lost while it should not be.
When a CR is detected, if the next byte is not LF, the CR byte should be
saved as the position point to the next byte (not LF). When a CR is
detected, if there is not yet other available bytes, the position is
reset to the position of CR (since a LF could follow).

A new Junit test case is added, using DECODER and variable number of CR
in the final attribute (testMultipartCodecWithCRasEndOfAttribute).

Result:
The attribute is now correctly decoded with the right number of CR
ending bytes.