Adding py3 support

It could use a more thorough test or example, but it works in both versions.  

```
kwhite@ghost:~/code/wempy$ echo 2.7.6 > .python-version && ./wempy <<-EOF

{{first_name = 'Tyler'}}

{{last_name = 'Durden'}}

Hello Mr. {{=last_name}} or shall I call you {{=first_name}} instead?

EOF





Hello Mr. Durden or shall I call you Tyler instead?

kwhite@ghost:~/code/wempy$ echo 3.4.0 > .python-version && ./wempy <<-EOF

{{first_name = 'Tyler'}}

{{last_name = 'Durden'}}

Hello Mr. {{=last_name}} or shall I call you {{=first_name}} instead?

EOF






Hello Mr. Durden or shall I call you Tyler instead?

```