Allow number of threads compiler uses to be configured.

Clean up compiler executable flags. Added "--prelude" to allow including another prelude, like empty.cr.

Fixed type lookup: types were looked up from "self", but they should be looked up from the matching def.

Don't automaticlly flush after print, it leads to poor performance (it's better if the user controls this)

Build system cleanup and release/stats options.

Use mkstemp instead of deprecated tmpnam.

Fix 'make crystal', .PHONY targets, don't assume . is in PATH.

Silence warnings from "which" correctly.

When using a union as a restriction, bind free variables  from left to right whiel discarding matching types

Add more samples