Breaking Changes

v4

When updating from version 3 to version 4, there are a few breaking changes:

one-variable assignment in range

range x := someSlice would set x to the value of the element in v3. In v4, x will be the index of the element. (Ranging over a channel didn't change.) See #158.
Runtime.Set()

In v3, Set() would initialise a new variable in the top scope if no variable with that name existed. In v4, Set() will return an error when trying to set a variable that doesn't exist. Let() now always sets a variable in the current scope (possibly shadowing an existing one in a parent scope). SetOrLet() will try to change the value of an existing variable and only initialize a new variable in the current scope, if the variable doesn't exist. LetGlobal() is like Let() but always acts on the top scope.
new keywords return, try, catch and builtins exec, ints, slice, array

return, try, catch, exec, ints, slice and array are now keywords or predefined identifiers. If you previously used return, try or catch, you will have to rename your variables. exec, ints, slice and array can technically be overwritten, but you should make sure not to name your things those words regardless.
OSFileSystemLoader only handles a single directory

Use loaders.Multi to load templates from multiple directories. See #128.
relative paths

Relative paths to templates are now handled correctly. See #127.