This commit fixes several crashes:
1. Serialising IEEE 754-2008 decimals as well as
   NaN and +-Inf for float and doubles crashed
2. Converting IEEE 754-2008 decimals as well as NaN and +-Inf
   for float and dobules from amqp to amqpl crashed

The 2nd crash looks as follows:
```
exception exit: {function_clause,
                    [{mc_amqpl,to_091,
                         [<<"decimal-32">>,{as_is,116,<<124,0,0,0>>}],
                         [{file,"mc_amqpl.erl"},{line,747}]},
                     {mc_amqpl,'-convert_from/3-lc$^2/1-2-',1,
                         [{file,"mc_amqpl.erl"},{line,155}]},
                     {mc_amqpl,convert_from,3,
                         [{file,"mc_amqpl.erl"},{line,155}]},
                     {mc,convert,3,[{file,"mc.erl"},{line,358}]},
                     {rabbit_channel,outgoing_content,2,
                         [{file,"rabbit_channel.erl"},{line,2649}]},
                     {rabbit_channel,handle_basic_get,7,
                         [{file,"rabbit_channel.erl"},{line,2636}]},
                     {rabbit_channel,handle_cast,2,
                         [{file,"rabbit_channel.erl"},{line,617}]},
                     {gen_server2,handle_msg,2,
                         [{file,"gen_server2.erl"},{line,1056}]}]}
```
The 2nd crash is fixed by omitting any `{as_is, _TypeCode, _Binary}`
values during AMQP 1.0 -> AMQP 0.9.1 conversion.
This will be documented in the conversion table.

In addition to fixing these crashes, this commit adds tests that
RabbitMQ is able to store and forward IEEE 754-2008 decimals.
IEEE 754-2008 decimals can be parsed and serialsed by RabbitMQ.
However, RabbitMQ doesn't support interpreting this values. For example,
they can't be used on the headers exchange or for AMQP filter
expressions.

(cherry picked from commit 5c318c8)