6.0.0: Extended match statement, annotations cleanup

• Added -q command line option which suppresses all diagnostic output
  from the compiler except for errors
  (@thekid)
• Removed support for using curly braces as offset (e.g. $value{0})
  (@thekid)
• Merged PR #92: Add support for explicit octal integer literal notation
  See https://wiki.php.net/rfc/explicit_octal_notation (PHP 8.1)
  (@thekid)
• Merged PR #93: Allow match without expression: match { ... }. See
  https://wiki.php.net/rfc/match_expression_v2#allow_dropping_true
  (@thekid)
• Removed support for legacy XP and Hack language annotations, see #86
  (@thekid)
• Merged PR #96: Enclose blocks where PHP only allows expressions. This
  not only allows fn() => { ... } but also using blocks in match.
  (@thekid)

5.7.0: Compile to XAR

• Verified full PHP 8 support now that PHP 8.0.0 has been released,
  see https://www.php.net/archive/2020.php#2020-11-26-3
  (@thekid)
• Merged PR #95: Support compiling to XAR archives - @thekid

5.6.0: PHP 8 feature completeness

• Merged PR #94: Add support for static return type - @thekid
• Optimized null-safe instance operator for PHP 8.0 - @thekid
• Added PHP 8.1-dev to test matrix now that is has been branched
  (@thekid)
• Added support for non-capturing catches, see this PHP 8 RFC:
  https://wiki.php.net/rfc/non-capturing_catches
  (@thekid)

5.5.0: Union and callable types

• Merged PR #91 - Refactor rewriting type literals:
  • Changed implementation to be easier to maintain
  • Emit function types as callable in all PHP versions
  • Emit union types as syntax in PHP 8+
    (@thekid)

5.4.1: PHP 8.0.0RC1 compatibility

• Fixed #90: Namespace declaration statement has to be the very first
  statement, which occured with PHP 8.0.0RC1
  (@thekid)

5.4.0: RFC 336

• Implemented second step for #86: Add an E_DEPRECATED warning to the
  hacklang annotation syntax <<...>>; details in xp-framework/ast#9
  (@thekid)
• Merged PR #89: Add annotation type mappings to TARGET_ANNO detail
  (@thekid)
• Changed PHP 8 attributes to be emitted in XP meta information without
  namespaces, and with their first characters lowercased. This way, code
  using annotations will continue to work, see xp-framework/rfc#336.
  (@thekid)

5.3.0: Named arguments for PHP 8

• Merged PR #88: Emit named arguments for PHP 8 - @thekid

5.2.1: AST library forward compatibility

• Adjusted to xp-framework/ast yielding comments as-is, transform
  them to the form XP meta information expects.
  (@thekid)

5.2.0: PHP 8 attributes, match and nullsafe operator

• Merged PR #87: Add support for match expression - @thekid
• Implemented first step of #86: Support PHP 8 attributes - @thekid
• Removed lang.ast.syntax.php.NullSafe in favor of builtin support
  (@thekid)
• Merged PR #84: Extract parser - @thekid

5.1.3: Allow ::class on objects

• Allowed ::class on objects (PHP 8.0 forward compatibility) - @thekid