Support base64 encoded property values

If a svn property contains certain characters (like control characters
or non-UTF8 ones, 0xe9 in this example), the svnlook proplist output
looks like:

  <?xml version="1.0" encoding="UTF-8"?>
  <properties>
  <target
     path="/a">
  <property
     encoding="base64"
     name="test2">6XgiCnkK
  </property>
  </target>
  </properties>

SVN::Look ignored the encoding="base64" attribute and the property in
the hash returned by proplist contains the base64 encode value.

This change fixes this.

Issue: https://github.com/gnustavo/SVN-Look/issues/3
Fix grokking of the 'svnlook changed' output

The unpack template we were using was stripping trailing spaces
from filenames.

Issue: https://github.com/gnustavo/SVN-Look/issues/4
Placate Perl::Critic
v0.40