update changelog so far

CHANGELOG.rst

 Changelog for MMLlib
 ====================
 
+1.5 (unreleased)
+----------------
+
+- Speed up parsing a little
+- Improve documentation
+- Formalise metadata reading and interpretation; key/value pairs
+  will now only be used if the first empty line-terminated block
+  is comprised of only metadata header lines (other comments must
+  move to below that first empty line)
+- Add “showmeta” command, without console_scripts entry though
+- Provide means to run a command without console_scripts entry,
+  to avoid $PATH pollution with many commands
+
 1.4
 ---