Implement XML builder

[qcam]

Roadmap:

• Encoding.
  • Prolog.
  • CDATA.
  • Comment.
  • Reference (character ref, entity ref).
  • Processing Instruction.
• Benchmark (Add benchmarking code for Encoder saxy-bench#1).
• XML builder interface.

[stevedomin]

Hi @qcam, any help needed to push this PR over the line?

[qcam]

hey @stevedomin, helps are always welcome! This is a draft to experiment around how XML encoding interface would look like.

I've updated the roadmap for this PR (I might miss something or perhaps it could be split into smaller parts). Are you interested in working on any item on the list?

[qcam]

First draft implemented. Benchmarking result was quite promising.

In comparison to xml_builder, the benchmark result on my local computer tells that Saxy encoder was about 9-10 times faster.

Operating System: macOS
CPU Information: Intel(R) Core(TM) i7-6567U CPU @ 3.30GHz
Number of Available Cores: 4
Available memory: 16 GB
Elixir 1.6.5
Erlang 20.3.4
Benchmark suite executing with the following configuration:
warmup: 2 s
time: 5 s
parallel: 1
inputs: none specified
Estimated total run time: 14 s


Benchmarking saxy...
Benchmarking xml_builder...

Name                  ips        average  deviation         median         99th %
saxy             489.38 K        2.04 μs  ±2443.12%           2 μs           7 μs
xml_builder       47.29 K       21.15 μs   ±101.08%          21 μs          49 μs

Comparison:
saxy             489.38 K
xml_builder       47.29 K - 10.35x slower