v2.6.0 Support for file specifications, several performance improvements

What's Changed

• Upgrade samples library to new version and move sample tests to their own folder by @PrinsFrank in #248
• Cache font widths on Font property as it will be called for every text element by @PrinsFrank in #250
• Decrease memory footprint contentStreamParser by not appending string in memory and reading from stream directly by @PrinsFrank in #251
• Fix font widths caching by setting property to false when no widths are available by @PrinsFrank in #252
• Search backwards from known start of next object positions for endobj/endstream markers instead of start current object by @PrinsFrank in #253
• AF dictionary key can be referenceValueArray by @PrinsFrank in #257
• Clean up old development documentation that is now outdated by @PrinsFrank in #258
• Add support for file specifications by @PrinsFrank in #259

Full Changelog: v2.5.1...v2.6.0