Fix usage of question mark. Not sure if this is what was intended but…

… seemed logical.

README.md

@@ -101,10 +101,16 @@ Coverlet gives the ability to have fine grained control over what gets excluded
 
 Syntax: `/p:Exclude=[Assembly-Filter]Type-Filter`
 
+Wildcards
+- `*` => matches zero or more characters
+- `?` => the prefixed character is optional
+
 Examples
  - `/p:Exclude="[*]*"` => Excludes all types in all assemblies (nothing is instrumented)
  - `/p:Exclude="[coverlet.*]Coverlet.Core.Coverage"` => Excludes the Coverage class in the `Coverlet.Core` namespace belonging to any assembly that matches `coverlet.*` (e.g `coverlet.core`)
  - `/p:Exclude="[*]Coverlet.Core.Instrumentation.*"` => Excludes all types belonging to `Coverlet.Core.Instrumentation` namespace in any assembly
+ - `/p:Exclude="[coverlet.*.tests?]*"` => Excludes all types in any assembly starting with `coverlet.` and ending with `.test` or `.tests` (the `?` makes the `s`  optional)
+ - `/p:Exclude="[coverlet.*]*,[*]Coverlet..Core*"` => Excludes assemblies matching `coverlet.*` and excludes all types belonging to the `Coverlet.Core` namespace in any assembly
 
 ```bash
 dotnet test /p:CollectCoverage=true /p:Exclude="[coverlet.*]Coverlet.Core.Coverage"

src/coverlet.core/Helpers/InstrumentationHelper.cs

@@ -107,7 +107,7 @@ public static bool IsValidFilterExpression(string filter)
             if (filter.EndsWith("]"))
                 return false;
 
-            if (new Regex(@"[^\w*]").IsMatch(filter.Replace(".", "").Replace("[", "").Replace("]", "")))
+            if (new Regex(@"[^\w*]").IsMatch(filter.Replace(".", "").Replace("?", "").Replace("[", "").Replace("]", "")))
                 return false;
 
             return true;
@@ -229,7 +229,7 @@ private static string WildcardToRegex(string pattern)
         {
             return "^" + Regex.Escape(pattern).
             Replace("\\*", ".*").
-            Replace("\\?", ".") + "$";
+            Replace("\\?", "?") + "$";
         }
 
         private static bool IsAssembly(string filePath)