Update lastEnd in tokenizer interface

The hack for parsing --> depends on it.

Closes #84
Add allowReturnOutsideFunction option

Issue #86
Don't complain about reserved words in property name position

Also add forbidReserved: "everywhere" support.

Issue #85
[walker] Supply ancestors to visitor functions
Mark version 0.5
Bump version number post-0.5
Renamed node_t to Node and exported it

This is to let programmers extend the Node object with utility methods
Rename remaining *_t constructors to something sane
Don't export Node from loose parser, reuse existing Node's proto

Issue #92
Prevent loose parser from tripping on invalid regexps

Issue #39
Updates license year
[loose parser] Fix interpretation of `f."`

Before this the ast produced by parse_dammit crashed in the following
code, as Uglify correctly noticed that f."" is invalid.

    sample = 'f."';

    loose = require('acorn/acorn_loose');
    uglify = require('uglify-js');

    out = new uglify.OutputStream();
    ast = loose.parse_dammit(sample);
    ast = uglify.AST_Node.from_mozilla_ast(ast);
    ast.print(out);
    // TypeError: Cannot call method 'toString' of undefined
    // member_exp.computed = false && member_exp.property == ""

    console.log(out.toString());

After this the round-tripped AST looks like: `t.✖;"";`, which is
consistent with how `foo.{` is parsed.

I also considered making it parse as t[""], but as this only turns up in
the wild when people try to use multiline strings, I felt it was better
to be obviously wrong.
Support rest parameters

http://wiki.ecmascript.org/doku.php?id=harmony:rest_parameters
The final parameter to a function is a rest parameter if it is
prefixed by "...". FunctionExpression and FunctionDeclaration
nodes have a new "rest" property that is null if there is no
rest parameter, or contains an Identifer for the parameter.
https://developer.mozilla.org/en-US/docs/SpiderMonkey/Parser_API#Functions

Implemented by adding a new token, `_ellipsis`, which consists of
three dots. Modified the body of parseFunction to allow a single
rest parameter at the end of an argument list. Both the token and
the rest parameter require `options.ecmaVersion` >= 6, otherwise
three dots are tokenized as three dots.
Add option: `--`

Had a few bugs in the initial patch request (#98) as well...

Also, fixed the help() command to print to stderr on nonzero exit statuses given.
Clean up previous patch

Issue #100
Minor: Remove unused argument from readToken_slash

Possible dev relic.

readToken_slash currently does not have any arguments and does not appear to look at arguments. All existing tests pass after removal of extraneous argument while calling readToken_slash.
Check duplicate argument names for rest params

Issue #79
Add note about browser compatibility to README

Closes #105
ecma 6 partial support: let and const
Note partial es6 support in docs