[BREAKING CHANGE] Field accessors should use property getters in C#

In C#, plain field accessors should not be nonparametric methods
but should be standard property getters.

The accessor methods with parameters were renamed to `GetXxx`
because a method cannot be named identically to a property.

Also, `ByteBuffer.Position`, `FlatBufferBuilder.Offset` and
`FlatBufferBuilder.DataBuffer` are now properties instead
of nonparametric accessor methods, for more idiomatic C# style.

This is a breaking change, all client C# code accessing these
fields needs to be changed (i.e. remove those `()` or add the
`Get` prefix).

Issue: #77
Change-Id: Iaabe9ada076e5ea2c69911cf6170fdda2df3487e

net/FlatBuffers/ByteBuffer.cs

@@ -17,7 +17,6 @@
 //#define UNSAFE_BYTEBUFFER  // uncomment this line to use faster ByteBuffer
 
 using System;
-using System.Linq;
 
 namespace FlatBuffers
 {
@@ -42,7 +41,7 @@ namespace FlatBuffers
             _pos = 0;
         }
 
-        public int position() { return _pos; }
+        public int Position { get { return _pos; } }
 
         // Pre-allocated helper arrays for convertion.
         private float[] floathelper = new[] { 0.0f };