Always use optimal encoding function

[ypconstante]

Floki today has two similar encoding functions, Floki.Entities.encode and Floki.RawHTML.html_escape.
This PR moves the html_escape code to the Entities module, ensuring we always use the fastest encoding function available.

##### With input big #####
Name                    ips        average  deviation         median         99th %
bench                 50.48       19.81 ms     ±8.35%       19.23 ms       26.89 ms
bench (today)         25.47       39.26 ms    ±10.21%       38.05 ms       55.82 ms

Comparison: 
bench                 50.48
bench (today)         25.47 - 1.98x slower +19.45 ms

Memory usage statistics:

Name             Memory usage
bench                 9.49 MB
bench (today)         9.23 MB - 0.97x memory usage -0.25281 MB

**All measurements for memory usage were the same**

##### With input medium #####
Name                    ips        average  deviation         median         99th %
bench                161.10        6.21 ms     ±9.48%        6.06 ms        9.19 ms
bench (today)         98.20       10.18 ms     ±7.52%        9.96 ms       13.76 ms

Comparison: 
bench                161.10
bench (today)         98.20 - 1.64x slower +3.98 ms

Memory usage statistics:

Name             Memory usage
bench                 3.31 MB
bench (today)         3.29 MB - 1.00x memory usage -0.01551 MB

**All measurements for memory usage were the same**

##### With input small #####
Name                    ips        average  deviation         median         99th %
bench                805.16        1.24 ms    ±10.37%        1.24 ms        1.73 ms
bench (today)        263.75        3.79 ms    ±31.24%        4.31 ms        5.99 ms

Comparison: 
bench                805.16
bench (today)        263.75 - 3.05x slower +2.55 ms

Memory usage statistics:

Name             Memory usage
bench               720.79 KB
bench (today)       710.66 KB - 0.99x memory usage -10.13281 KB

read_file = fn name ->
  __ENV__.file
  |> Path.dirname()
  |> Path.join(name)
  |> File.read!()
  |> Floki.parse_document!()
end

inputs = %{
  "big" => read_file.("big.html"),
  "medium" => read_file.("medium.html"),
  "small" => read_file.("small.html")
}

Benchee.run(
  %{
    "bench" => &Floki.raw_html/1
  },
  time: 10,
  inputs: inputs,
  memory_time: 2
)

[philss]

🚀

[philss]

Nice catch! Thank you!