Add support for crescendo and decrescendo in alphaTex (#338)

* Added crescendo/decrescendo parsing to alphaTex

* Added docs for crescendo

Author: Danielku15

Documentation/input/alphatex/beat-effects.cshtml

@@ -6,7 +6,7 @@ TexSample: true
 <p>
 	There are various effects that can be applied to a beat. All beat
 	effects are specified in braces after the beat. 
-	<code>Beat{Effects}</code>
+	<code>Beat{Effects}</code> Multiple effects are simple separated by spaces like <code>3.3 {f v}</code>
 </p>    
 
 <h2 id="simple-effects">Simple Effects</h2>
@@ -48,6 +48,9 @@ TexSample: true
 |
 // tremolo picking (`tp duration` where duration can be 8,16 or 32)
 3.3{tp 8} 3.3{tp 16} 3.3{tp 32}
+|
+// Crescendo / Decrescendo
+3.3{cre} 3.3{cre} 3.3{dec} 3.3{dec}
 </div>
 <script type="text/x-alphatab">
 	$('#alphaTabBeatEffects').alphaTab();

Source/AlphaTab.Test/Importer/AlphaTexImporterTest.cs

@@ -967,5 +967,15 @@ public void TestDynamics()
         }
 
 
+        [TestMethod]
+        public void TestCrescendo()
+        {
+            var tex = @"1.1.4{dec} 1.1{dec} 1.1{cre} 1.1{cre}";
+            var score = ParseTex(tex);
+            Assert.AreEqual(CrescendoType.Decrescendo, score.Tracks[0].Staves[0].Bars[0].Voices[0].Beats[0].Crescendo);
+            Assert.AreEqual(CrescendoType.Decrescendo, score.Tracks[0].Staves[0].Bars[0].Voices[0].Beats[1].Crescendo);
+            Assert.AreEqual(CrescendoType.Crescendo, score.Tracks[0].Staves[0].Bars[0].Voices[0].Beats[2].Crescendo);
+            Assert.AreEqual(CrescendoType.Crescendo, score.Tracks[0].Staves[0].Bars[0].Voices[0].Beats[3].Crescendo);
+        }
     }
 }

Source/AlphaTab/Importer/AlphaTexImporter.cs

@@ -1535,6 +1535,20 @@ private bool ApplyBeatEffect(Beat beat)
                 return true;
             }
 
+            if (syData == "cre")
+            {
+                beat.Crescendo = CrescendoType.Crescendo;
+                NewSy();
+                return true;
+            }
+            
+            if (syData == "dec")
+            {
+                beat.Crescendo = CrescendoType.Decrescendo;
+                NewSy();
+                return true;
+            }
+
             if (syData == "tp")
             {
                 NewSy();