feat: force encoding

[abemedia]

Closes #93

• Write tests
• Add doc string
• Update readme

[github-actions]

Benchmark Results

.

goos: linux
goarch: amd64
pkg: github.com/abemedia/go-don
cpu: Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz
                         │   before    │               after                │
                         │   sec/op    │   sec/op     vs base               │
Handler/Request-2          342.8n ± 1%   338.6n ± 0%  -1.21% (p=0.001 n=10)
Handler/RequestPointer-2   361.3n ± 0%   360.0n ± 0%       ~ (p=0.065 n=10)
geomean                    351.9n        349.2n       -0.78%

                         │   before   │                after                │
                         │    B/op    │    B/op     vs base                 │
Handler/Request-2          24.00 ± 0%   24.00 ± 0%       ~ (p=1.000 n=10) ¹
Handler/RequestPointer-2   24.00 ± 0%   24.00 ± 0%       ~ (p=1.000 n=10) ¹
geomean                    24.00        24.00       +0.00%
¹ all samples are equal

                         │   before   │                after                │
                         │ allocs/op  │ allocs/op   vs base                 │
Handler/Request-2          1.000 ± 0%   1.000 ± 0%       ~ (p=1.000 n=10) ¹
Handler/RequestPointer-2   1.000 ± 0%   1.000 ± 0%       ~ (p=1.000 n=10) ¹
geomean                    1.000        1.000       +0.00%
¹ all samples are equal

[codecov]

Codecov Report

Patch coverage: 80.00% and project coverage change: -0.47 ⚠️

Comparison is base (7b4ccb9) 98.35% compared to head (358cc9b) 97.89%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #146      +/-   ##
==========================================
- Coverage   98.35%   97.89%   -0.47%     
==========================================
  Files          24       24              
  Lines         850      854       +4     
==========================================
  Hits          836      836              
- Misses          9       11       +2     
- Partials        5        7       +2     

Impacted Files	Coverage Δ
api.go	94.87% <80.00%> (-5.13%)	⬇️

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