Replaced the NotImplementedException from ToUnit with UnitNotFoundException (#1594)

- moved all exceptions into a new solution folder
- replaced the `NotImplementedException` which is thrown from the
`ToUnit` method with `UnitNotFoundException`

---------

Co-authored-by: Andreas Gullberg Larsen <andreas.larsen84@gmail.com>

Author: lipchev

CodeGen/Generators/NanoFrameworkGen/QuantityGenerator.cs

@@ -202,7 +202,7 @@ private double GetValueInBaseUnit()
             }
 
             Writer.WL($@"
-                        _ => throw new NotImplementedException($""Can not convert {{Unit}} to base units."")
+                        _ => throw new NotImplementedException($""Can't convert {{Unit}} to base units."")
                     }};
                     }}
 
@@ -223,7 +223,7 @@ private double GetValueAs({_unitEnumName} unit)
             }
 
             Writer.WL(@"
-                        _ => throw new NotImplementedException($""Can not convert {Unit} to {unit}."")
+                        _ => throw new NotImplementedException($""Can't convert {Unit} to {unit}."")
                     };
                     }
 

CodeGen/Generators/UnitsNetGen/QuantityGenerator.cs

@@ -100,7 +100,7 @@ namespace UnitsNet
 }}");
             return Writer.ToString();
         }
-        
+
         private void GenerateInterfaceExtensions()
         {
             // generate the base interface (either IVectorQuantity, IAffineQuantity or ILogarithmicQuantity)
@@ -158,7 +158,7 @@ private void GenerateInterfaceExtensions()
         IEquatable<{_quantity.Name}>,
         IFormattable");
         }
-        
+
         private void GenerateQuantityInfo()
         {
             var quantityInfoClassName = $"{_quantity.Name}Info";
@@ -1081,7 +1081,7 @@ public double As(UnitSystem unitSystem)
             else
             {{
                 // No possible conversion
-                throw new NotImplementedException($""Can not convert {{Unit}} to {{unit}}."");
+                throw new UnitNotFoundException($""Can't convert {{Unit}} to {{unit}}."");
             }}
         }}