update header file comments (closes #157)

utf8proc.c

@@ -1,6 +1,6 @@
 /* -*- mode: c; c-basic-offset: 2; tab-width: 2; indent-tabs-mode: nil -*- */
 /*
- *  Copyright (c) 2018 Steven G. Johnson, Jiahao Chen, Peter Colberg, Tony Kelman, Scott P. Jones, and other contributors.
+ *  Copyright (c) 2014-2019 Steven G. Johnson, Jiahao Chen, Peter Colberg, Tony Kelman, Scott P. Jones, and other contributors.
  *  Copyright (c) 2009 Public Software Group e. V., Berlin, Germany
  *
  *  Permission is hereby granted, free of charge, to any person obtaining a

utf8proc.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018 Steven G. Johnson, Jiahao Chen, Peter Colberg, Tony Kelman, Scott P. Jones, and other contributors.
+ * Copyright (c) 2014-2019 Steven G. Johnson, Jiahao Chen, Peter Colberg, Tony Kelman, Scott P. Jones, and other contributors.
  * Copyright (c) 2009 Public Software Group e. V., Berlin, Germany
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
@@ -27,8 +27,8 @@
  *
  * utf8proc is a free/open-source (MIT/expat licensed) C library
  * providing Unicode normalization, case-folding, and other operations
- * for strings in the UTF-8 encoding, supporting Unicode version
- * 9.0.0.  See the utf8proc home page (http://julialang.org/utf8proc/)
+ * for strings in the UTF-8 encoding, supporting up-to-date Unicode versions.
+ * See the utf8proc home page (http://julialang.org/utf8proc/)
  * for downloads and other information, or the source code on github
  * (https://github.com/JuliaLang/utf8proc).
  *