Add support for parsing multiple types of quotation marks in commands, Fix #942 (#943)

* Add ability to support different types of quotation marks

* Added normal quotation mark to list of aliases, removed single quote mark

* clean up leftover changes from testing

* change quotation mark parsing to use a map of matching pairs

* remove commented out code

* Fix conventions of the command parser utility functions

* change storage type of alias dictionary to be IReadOnlyDictionary

* revert type of CommandServiceConfig QuotationMarkAliasMap to Dictionary

* minor formatting changes to CommandParser

* remove unnecessary whitespace

* Move aliases outside of CommandInfo class

* copy IReadOnlyDictionary to ImmutableDictionary

* minor syntax changes in CommandServiceConfig

* add newline before namespace for consistency

* newline formatting tweak

* simplification of GetMatch method for CommandParser

* add more quote unicode punctuation pairs

* add check for null value when building ImmutableDictionary

* Move default alias map into a separate source file

* Ensure that the collection passed into command service is not null

src/Discord.Net.Commands/CommandService.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Collections.Immutable;
@@ -32,6 +32,7 @@ namespace Discord.Commands
         internal readonly RunMode _defaultRunMode;
         internal readonly Logger _cmdLogger;
         internal readonly LogManager _logManager;
+        internal readonly IReadOnlyDictionary<char, char> _quotationMarkAliasMap;
 
         public IEnumerable<ModuleInfo> Modules => _moduleDefs.Select(x => x);
         public IEnumerable<CommandInfo> Commands => _moduleDefs.SelectMany(x => x.Commands);
@@ -45,6 +46,7 @@ namespace Discord.Commands
             _ignoreExtraArgs = config.IgnoreExtraArgs;
             _separatorChar = config.SeparatorChar;
             _defaultRunMode = config.DefaultRunMode;
+            _quotationMarkAliasMap = (config.QuotationMarkAliasMap ?? new Dictionary<char, char>()).ToImmutableDictionary();
             if (_defaultRunMode == RunMode.Default)
                 throw new InvalidOperationException("The default run mode cannot be set to Default.");
 
@@ -337,7 +339,6 @@ namespace Discord.Commands
         public async Task<IResult> ExecuteAsync(ICommandContext context, string input, IServiceProvider services, MultiMatchHandling multiMatchHandling = MultiMatchHandling.Exception)
         {
             services = services ?? EmptyServiceProvider.Instance;
-
             var searchResult = Search(context, input);
             if (!searchResult.IsSuccess)
                 return searchResult;