Check that compiler error are user always user friendly

Signed-off-by: Julien Danjou <julien@danjou.info>
Write a test for builds() check

Signed-off-by: Julien Danjou <julien@danjou.info>
Modify HyDict semantics to allow nesting expressions

HyDicts are now HyLists, that get compiled down to dicts
only by the compiler.
Add tests for expr-in-dict
Test quoting dicts
Merge branch 'master' into pr/177
style fix - long line
Merge branch 'master' into pr/179
Merge branch 'master' into pr/182