Add method: FixMessage.getByIndex(int index)

[kpavlov]

let the program know the exact order of the individual tags on incoming messages and to control the exact order of the individual tags on outgoing messages. some FIX gateways I have seen mandate an exact order of the individual fix tags and will reject messages. We all know the FIX protocol allows tags in any order but numerous systems cannot handle tags not the desired order

comment by Robert J Wolf.

Field order is defined by their insertion order in FixMessageBuilder, and by order of appearance in the stream for FixMessage due to Fields are stored in ArrayList internally. To ensure field order in outgoing message, please add them to FixMessageBuilder in that order.

Add a method to fetch a field by index, something like: FixMessageFragment FixMessage.getByIndex(int index)

Index should be absolute (not relative to message body).