Add logging (#13)

* Started adding logging

* Fixed warnings

* Added RegexBuilderLoggingTest

* Added RegexBuilderDslLoggingTest

* Updated README.md

Author: markwhitaker

README.md

@@ -14,7 +14,49 @@ It offers a lot of benefits over using raw regex syntax in strings:
 
 It is fully documented in the [project wiki](https://github.com/markwhitaker/RegexToolbox.kt/wiki).
 
-## New in version 2.0
+## New in 2.2
+
+### Logging
+
+Use the new `addLogger()` method to connect a logger of your choice and see how your regex is built, step by step. For example:
+
+```kotlin
+val regex = RegexBuilder()
+    .addLogger {
+        println(it)
+    }
+    .wordBoundary()
+    .text("Regex")
+    .anyOf("Builder", "Toolbox")
+    .wordBoundary()
+    .buildRegex()
+```
+
+or this:
+
+```kotlin
+val regex = regex {
+    addLogger {
+        println(it)
+    }
+    wordBoundary()
+    text("Regex")
+    anyOf("Builder", "Toolbox")
+    wordBoundary()
+}
+```
+
+will output this to your console:
+
+```text
+RegexBuilder: wordBoundary(): \b
+RegexBuilder: text("Regex"): Regex
+RegexBuilder: anyOf("Builder", "Toolbox"): (?:Builder|Toolbox)
+RegexBuilder: wordBoundary(): \b
+RegexBuilder: buildRegex(): \bRegex(?:Builder|Toolbox)\b
+```
+
+## New in 2.0
 
 ### New builder syntax
 

build.gradle

@@ -1,5 +1,6 @@
 buildscript {
     ext.junit_version = '4.12'
+    ext.mockk_version = '1.9.3.kotlin12'
 }
 
 plugins {
@@ -24,6 +25,7 @@ sourceCompatibility = 1.8
 dependencies {
     implementation 'org.jetbrains.kotlin:kotlin-stdlib-jdk8'
     testImplementation "junit:junit:$junit_version"
+    testImplementation "io.mockk:mockk:$mockk_version"
 }
 
 compileKotlin {