A few cleanups

[johnnychen94]

This commit picks the result from JuliaImages/ImageInTerminal.jl#62

(Not yet done) In the spirit of LazyModules, we might also want to make the final API depends on basic Base types:

xterm_24bit_encode(img; kwargs...)
xterm_24bit_encode(io::IO, img; small_block=true)

Curiously, @t-bltg I noticed that you have explicitly changed a few IOBuffer usages to PipeBuffer in many places, what's the benefit of PipeBuffer over IOBuffer?

[codecov]

Codecov Report

Merging #3 (5d9210d) into master (4f06b40) will decrease coverage by 2.93%.
The diff coverage is 91.11%.

❗ Current head 5d9210d differs from pull request most recent head f4494fa. Consider uploading reports for the commit f4494fa to get more accurate results

@@            Coverage Diff             @@
##           master       #3      +/-   ##
==========================================
- Coverage   98.09%   95.16%   -2.94%     
==========================================
  Files           3        4       +1     
  Lines         105      124      +19     
==========================================
+ Hits          103      118      +15     
- Misses          2        6       +4     

Impacted Files	Coverage Δ
src/utils.jl	71.42% <71.42%> (ø)
src/colors.jl	93.54% <93.54%> (ø)
src/XTermColors.jl	100.00% <100.00%> (ø)
src/encoder.jl	97.36% <100.00%> (ø)

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[t-bltg]

Curiously, @t-bltg I noticed that you have explicitly changed a few IOBuffer usages to PipeBuffer in many places, what's the benefit of PipeBuffer over IOBuffer?

PipeBuffer is a simplified IOBuffer which does not support moving the cursor position (seek, ...). I think it's more performant, but I haven't tested it for perf. It simplifies the code such as https://github.com/JuliaLang/julia/blob/c298e4ee996c4d52a0ceb17c209831042f72e6c0/test/iobuffer.jl#L152: read(io, String) for a Pipebuffer vs String(take!(io)) for a IOBuffer.

[johnnychen94]

I'll continue or follow up your devs the next day, so let me merge this first.