pretty printing is wrong for tabs

[jyn514]

Tabs should be normalized to (4 or 8) spaces before printing; tabs should count as (4 or 8) characters when calculating comments.

void f() {
	void g() { return 1; }
	return;
}
<stdin>:2:7: error: invalid program: functions cannot be nested. hint: try declaring g as `static` at file scope
	void g() { return 1; }
      ^

[jyn514]

https://github.com/brendanzab/codespan/pull/82/files looks helpful