pkg/math: add Ceil and Trunc
Merge branch 'master' of github.com:axw/llgo
Implement method values

Go 1.1 method values are now supported.

Converting a method to a function (i.e. with no receiver)
triggers method value assignment. There's a fair bit of
overlap with how concrete methods are assigned to interface
functions, so this needs to be refactored at some stage.

Fixes #63
Fixes #64
Fixes #66
Fixes #67