Allow BMS encoding to be specified through filename.

[dtinth]

Rationale:

Character set detection is sometimes inaccurate. To allow overriding the encoding without changing content, creators can specify the encoding of the file through file naming.

• .utf8.bms — Always read as UTF-8
• .sjis.bms — Always read as Shift-JIS
• .euc_kr.bms — Always read as EUC-KR

Tasks:

• bms-js
  • getReaderOptionsFromFilename
  • Implement reader options
  • Publish 3.1.0-1
• bemuse-notechart
  • NotechartLoader — pass filename
  • Publish
• bemuse-indexer
  • readBMS — pass filename
  • Publish
• bemuse
  • Update bemuse-notechart and bemuse-indexer

[codecov-io]

Codecov Report

Merging #492 into master will increase coverage by 0.01%.
The diff coverage is 91.66%.

@@            Coverage Diff            @@
##           master    #492      +/-   ##
=========================================
+ Coverage   84.09%   84.1%   +0.01%     
=========================================
  Files         170     171       +1     
  Lines        5370    5387      +17     
  Branches        1       1              
=========================================
+ Hits         4516    4531      +15     
- Misses        854     856       +2

Impacted Files	Coverage Δ
packages/bms/spec/reader_spec.js	100% <100%> (ø)	⬆️
packages/bemuse-notechart/src/loader/index.js	100% <100%> (ø)	⬆️
packages/bemuse-indexer/src/index.js	93.8% <100%> (+0.05%)	⬆️
packages/bms/src/reader/index.js	85% <100%> (+3.75%)	⬆️
...ges/bms/src/reader/getReaderOptionsFromFilename.js	75% <75%> (ø)

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