Erlang 25.0 removes the ability to load modules compiled prior to Erlang
22.0. This patch replaces the Jiffy's `enc` based build system with the
`rebar3` port compiler plugin for Erlang 25.0 and newer.

2c92afb029

Compiled with the oldest supported OTP R15B03-1

Thought slightly harder and realized this was unnecessary.

Turns out this was never implemented correctly since it was referring to
the original bytes_per_iter atom.

The recent release of Erlang 23.0 removed support for loading beam
modules compiled under R14 and earlier. Thus we're now forced to abandon
support for R13 and R14.

This bug was due to an interaction between two optimizations. If we
attempt to flush the buffer before any bytes are used we refused.
However, in enc_ensure we were not checking whether the buffer was
actually flushed so we would allocate a new buffer for the request.

The easiest way to encounter this issue was by encoding a raw binary
longer than 2041 bytes (i.e., `jiffy:encode(<<"stuff...">>).`).

This adds a dynamic check to see if -flto is supported by the compiler.

Co-Authored-By: JianBo He <heeejianbo@gmail.com>

Apparently Travis-CI has dropped some of the older Erlang versions. I've
also added a run on 22.x

Co-Authored-By: Stephan Renatus <srenatus@chef.io>

We don't do fishy things like type punning so it really isn't
necessary, and supplying it prevents certain optimizations.

This greatly increases the performance of long string encodes as
we won't need to copy intermediate results over and over.

If the input contained a mismatched end-of-array/object, the stack
could become empty before a call to dec_curr, which would look
beyond the bounds of the stack. If the value at this invalid
position happened to be st_array, we would pop too much from the
stack and overwrite the data that came before it.

This commit fixes this by letting dec_pop return the previous
state or st_invalid if the stack is empty, letting us exit
gracefully if the state isn't what we expect it to be.

dec_pop_assert is identical to the old dec_pop, tearing down the
emulator on internal errors.

This is a wee bit more cache-friendly than using a std::set with
string keys.

We requested atoms in latin1 and then handled them as utf-8,
erroring out on some valid atoms and performing pointless
validation on others.

enif_get_list_cell fails when the list is empty.