feature: add changelog to about dialog

changelog.txt

@@ -0,0 +1,16 @@
+
+Next Version
+* Feature: Add changelog.
+* Fix:     When the range sliders are overlapping the end slider cannot be moved.
+* Feature: Get version number from git tags.
+* Feature: You can now "follow" a file. When enabled the file is automatically reloaded
+           and scrolled to the end. Any manual scroll action disables "follow" mode.
+* Feature: Better support for fonts and characters with non-uniform width.
+* Fix:     Cannot scroll to arbitrary positions in a file if the file is larger than 2GB
+* Feature: File type specific highlighters.
+
+0.2.1
+* Feature: Show how many bytes are selected.
+* Feature: Highlighters can be disabled.
+* Feature: If a regex contains a group, then only the group is highlighted.
+           Using a filter expression like '(\d+)ms' will only hightlight the number.