Use a whitelisting model for configuring which rules to use.

This PR makes it possible to enable/disable specific rules for linting and formatting. Example configuration file:

{
  "blankLineBetweenMembers" : {
    "ignoreSingleLineProperties" : true
  },
  "indentation" : {
    "spaces" : 2
  },
  "lineLength" : 100,
  "maximumBlankLines" : 1,
  "respectsExistingLineBreaks" : true,
  "rules" : {
    "AllPublicDeclarationsHaveDocumentation" : true,
    "AlwaysUseLowerCamelCase" : false,
    "AmbiguousTrailingClosureOverload" : true,
    "AvoidInitializersForLiterals" : true,
    "BeginDocumentationCommentWithOneLineSummary" : true,
    "BlankLineBetweenMembers" : true,
    "CaseIndentLevelEqualsSwitch" : true,
    "DoNotUseSemicolons" : true,
    "DontRepeatTypeInStaticProperties" : true,
    "FullyIndirectEnum" : true,
    "GroupNumericLiterals" : true,
    "IdentifiersMustBeASCII" : true,
    "MultiLineTrailingCommas" : true,
    "NeverForceUnwrap" : true,
    "NeverUseForceTry" : true,
    "NeverUseImplicitlyUnwrappedOptionals" : true,
    "NoAccessLevelOnExtensionDeclaration" : true,
    "NoBlockComments" : false,
    "NoCasesWithOnlyFallthrough" : true,
    "NoEmptyAssociatedValues" : true,
    "NoEmptyTrailingClosureParentheses" : true,
    "NoLabelsInCasePatterns" : true,
    "NoLeadingUnderscores" : true,
    "NoParensAroundConditions" : true,
    "NoVoidReturnOnFunctionSignature" : true,
    "OneCasePerLine" : true,
    "OneVariableDeclarationPerLine" : true,
    "OnlyOneTrailingClosureArgument" : true,
    "OrderedImports" : true,
    "ReturnVoidInsteadOfEmptyTuple" : true,
    "UseEnumForNamespacing" : true,
    "UseLetInEveryBoundCaseVariable" : true,
    "UseOnlyUTF8" : true,
    "UseShorthandTypeNames" : false,
    "UseSingleLinePropertyGetter" : true,
    "UseSpecialEscapeSequences" : true,
    "UseSynthesizedInitializer" : true,
    "UseTripleSlashForDocumentationComments" : true,
    "ValidateDocumentationComments" : true
  },
  "tabWidth" : 8,
  "version" : 1
}

If a rule is marked false, or if it is missing from the list, it will not be used for formatting or linting. All rules are enabled when running with default settings (i.e. not specifying a configuration file).

google / swift

Use a whitelisting model for configuring which rules to use. #235