Stop get_by_id traversal on first match

[ypconstante]

Today get_by_id just calls Finder.find and gets the first item in the list.
This PR refactors this method to avoid the unnecessary checks on match? and check the id value directly, and to stop the traversal on the first matching element.

Benchee.run(
  %{
    "get_by_id - beginning document" => fn doc -> Floki.get_by_id(doc, "mw-page-base") end,
    "get_by_id - end document" => fn doc -> Floki.get_by_id(doc, "footer-poweredbyico") end
  },
  time: 10,
  inputs: inputs,
  save: [path: "benchs/results/finder-#{tag}.benchee", tag: tag],
  memory_time: 2
)

##### With input big #####
Name                                                          ips        average  deviation         median         99th %
get_by_id - beginning document (PR)                      691.49 K     0.00145 ms  ±2360.83%     0.00124 ms     0.00233 ms
get_by_id - end document (PR)                              1.36 K        0.74 ms    ±11.08%        0.70 ms        1.09 ms
get_by_id - beginning document (v0.36.2-6-gb04be56)        0.75 K        1.33 ms     ±9.20%        1.29 ms        1.88 ms
get_by_id - end document (v0.36.2-6-gb04be56)              0.75 K        1.34 ms     ±9.00%        1.30 ms        1.89 ms

Comparison: 
get_by_id - beginning document (PR)                      691.49 K
get_by_id - end document (PR)                              1.36 K - 509.97x slower +0.74 ms
get_by_id - beginning document (v0.36.2-6-gb04be56)        0.75 K - 922.09x slower +1.33 ms
get_by_id - end document (v0.36.2-6-gb04be56)              0.75 K - 925.15x slower +1.34 ms

Memory usage statistics:

Name                                                   Memory usage
get_by_id - beginning document (PR)                             0 B
get_by_id - end document (PR)                                   0 B - 1.00x memory usage +0 B
get_by_id - beginning document (v0.36.2-6-gb04be56)           120 B - ∞ x memory usage +120 B
get_by_id - end document (v0.36.2-6-gb04be56)                 120 B - ∞ x memory usage +120 B

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

##### With input medium #####
Name                                                          ips        average  deviation         median         99th %
get_by_id - beginning document (PR)                      740.60 K        1.35 μs  ±2586.25%        1.17 μs        1.79 μs
get_by_id - end document (PR)                              3.78 K      264.49 μs    ±12.71%      253.67 μs      432.10 μs
get_by_id - beginning document (v0.36.2-6-gb04be56)        2.16 K      462.08 μs    ±12.16%      442.41 μs      711.64 μs
get_by_id - end document (v0.36.2-6-gb04be56)              2.16 K      462.52 μs    ±12.39%      446.88 μs      727.15 μs

Comparison: 
get_by_id - beginning document (PR)                      740.60 K
get_by_id - end document (PR)                              3.78 K - 195.88x slower +263.14 μs
get_by_id - beginning document (v0.36.2-6-gb04be56)        2.16 K - 342.22x slower +460.73 μs
get_by_id - end document (v0.36.2-6-gb04be56)              2.16 K - 342.54x slower +461.17 μs

Memory usage statistics:

Name                                                   Memory usage
get_by_id - beginning document (PR)                             0 B
get_by_id - end document (PR)                                   0 B - 1.00x memory usage +0 B
get_by_id - beginning document (v0.36.2-6-gb04be56)           120 B - ∞ x memory usage +120 B
get_by_id - end document (v0.36.2-6-gb04be56)                 120 B - ∞ x memory usage +120 B

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

##### With input small #####
Name                                                          ips        average  deviation         median         99th %
get_by_id - beginning document (PR)                      690.85 K        1.45 μs  ±1595.44%        1.29 μs        1.73 μs
get_by_id - end document (PR)                             17.30 K       57.80 μs    ±20.12%       54.98 μs      110.33 μs
get_by_id - end document (v0.36.2-6-gb04be56)              9.88 K      101.18 μs    ±20.39%       93.89 μs      190.50 μs
get_by_id - beginning document (v0.36.2-6-gb04be56)        9.88 K      101.20 μs    ±19.41%       93.79 μs      180.39 μs

Comparison: 
get_by_id - beginning document (PR)                      690.85 K
get_by_id - end document (PR)                             17.30 K - 39.93x slower +56.35 μs
get_by_id - end document (v0.36.2-6-gb04be56)              9.88 K - 69.90x slower +99.73 μs
get_by_id - beginning document (v0.36.2-6-gb04be56)        9.88 K - 69.92x slower +99.76 μs

Memory usage statistics:

Name                                                   Memory usage
get_by_id - beginning document (PR)                             0 B
get_by_id - end document (PR)                                   0 B - 1.00x memory usage +0 B
get_by_id - end document (v0.36.2-6-gb04be56)                 120 B - ∞ x memory usage +120 B
get_by_id - beginning document (v0.36.2-6-gb04be56)           120 B - ∞ x memory usage +120 B

[philss]

Cool! Thanks! :D