Files with shebang support?

Recast fail to parse files with a shebang impeaching its use on node bin files:
```
#! /usr/bin/env node

console.log('hello');
```

I will probably use a regExp to match and strip it in the meanwhile but i think it would be nice to have it in the core.

FYI I found the same kind of issues while trying to find one in this project: https://github.com/es-analysis/plato/issues/66

FYI till:
```
function _stripShebang(content) {
if(/#! (\/\w+)+ node/.test(content)) {
log('debug', 'Found a shebang, commenting it', path);
content = '// Shebang commented by xxxx: ' + content;
}
return content;
}
```

Start by reproducing the failure with the shebang-containing Node example from the issue and compare it with the same file without the shebang. Done means Recast parses the example without requiring the caller-side stripping workaround described in the report.

Written by the indexing model from the issue text.