[Speed] Add buffer to BinaryReader

[yaslab]

Improved speed of reading from file. (6a18924, 028bd2f)

Result of the performance test

• OS: Ubuntu 16.04
• Swift: 4.2.1-RELEASE
• Build Configuration: release
• CSV file info
  • File size: 13.3MB (15310 records, 55 fields)
  • Encoding: UTF-8 (Including ASCII and Japanese)

	Before (v2.2.1)	After (this branch)	Delta
1st	35.313s	5.811s	-83.5%
2nd	35.964s	5.746s	-84.0%
3rd	35.672s	5.732s	-83.9%

Test code

// main.swift
import Foundation
import CSV

let stream = InputStream(fileAtPath: "/path/to/file.csv")!
let csv = try! CSVReader(stream: stream, hasHeaderRow: true)
while csv.next() != nil {}

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@329bf23). Click here to learn what that means.
The diff coverage is 92.14%.

@@            Coverage Diff            @@
##             master      #65   +/-   ##
=========================================
  Coverage          ?   96.17%           
=========================================
  Files             ?       12           
  Lines             ?     1149           
  Branches          ?        0           
=========================================
  Hits              ?     1105           
  Misses            ?       44           
  Partials          ?        0

Impacted Files	Coverage Δ
Tests/CSVTests/CSVReaderTests.swift	100% <ø> (ø)
Sources/CSV/CSVReader.swift	96.38% <ø> (ø)
Tests/CSVTests/UnicodeTests.swift	100% <100%> (ø)
Sources/CSV/CSVWriter.swift	91.48% <100%> (ø)
Sources/CSV/BinaryReader.swift	85.91% <90.62%> (ø)
Tests/CSVTests/BinaryReaderTests.swift	92.64% <92.64%> (ø)

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[yaslab]

This branch can not be built by 1e83c6e. I will fix it with another PR.