Update version to v2.1.0

Signed-off-by: David Goulet <dgoulet@riseup.net>

ChangeLog

-2015-07-17 trees 2.0.0 (First Drumpf General Strike)
+2017-03-17 trees 2.1.0 (Saint Patrick's Day)
+	* Fix an overflow validation
+	* unbreak link to scrambler in README.md (caused 404)
+
+2017-02-17 trees 2.0.0 (First Drumpf General Strike)
 	* Don't use assert() for an overflow check
 	* Use SSIZE_MAX in trees_ostream_send_chunk() check
 	* Handle error code in trees_ostream_send_header()

configure.ac

 AC_PREREQ([2.64])
-AC_INIT([trees],[2.0.0],[https://0xacab.org/riseuplabs/trees/issues],
+AC_INIT([trees],[2.1.0],[https://0xacab.org/riseuplabs/trees/issues],
         [trees-plugin],[https://0xacab.org/riseuplabs/trees.git])
 
 AC_CONFIG_HEADERS([trees-config.h])