Handwritten parser

This subjective and opinionated patch fixes many issues but has
several drawbacks.

The parser should be usable in strict mode now (see #9). It is not
longer generated by `jison`. `parse.js` contains a simple handwritten
recursive decent parser. It should be easier to debug and to hack, but
there is definitely more code and one can prefer parser generators.
Note that `jison` seems to have big maintainance issues.

Note that [Yargs](https://github.com/yargs/yargs) is not usable in strict mode because it depends on
this package.

I also simplified the lexer (IMHO).

I wrote more Mocha-based tests in `test/index.js`. I really like the
embedded tests in `README.md`, but I was afraid to bloat it with
boring spec-compliance tests.

This patch does not introduce a breaking change and does not change
dependencies (however, it changes devDependencies).

Author: motet-a

.gitignore

@@ -1 +1 @@
-parser.js
+/node_modules/

.travis.yml

@@ -8,6 +8,7 @@ node_js:
 - "5"
 - "6"
 - "7"
+- "8"
 - "node"
 script:
 - "npm test"

AUTHORS

@@ -1,3 +1,4 @@
 C. Scott Ananian <cscott@cscott.net> (http://cscott.net)
 Kyle E. Mitchell <kyle@kemitchell.com> (https://kemitchell.com)
 Shinnosuke Watanabe <snnskwtnb@gmail.com>
+Antoine Motet <antoine.motet@gmail.com>

README.md

@@ -1,4 +1,4 @@
-This package parses SPDX license expression strings describing license terms, like [package.json license strings](https://docs.npmjs.com/files/package.json#license), into consistently structured ECMAScript objects.  The npm command-line interface depends on this package, as do many automatic license-audit tools.
+This package parses [SPDX license expression](https://spdx.org/spdx-specification-21-web-version#h.jxpfx0ykyb60) strings describing license terms, like [package.json license strings](https://docs.npmjs.com/files/package.json#license), into consistently structured ECMAScript objects.  The npm command-line interface depends on this package, as do many automatic license-audit tools.
 
 In a nutshell:
 

index.js

@@ -1,8 +1,6 @@
-var Scanner = require('./scanner')
-var Parser = require('./parser').Parser
+var scan = require('./scan')
+var parse = require('./parse')
 
-module.exports = function (string) {
-  var parser = new Parser()
-  parser.lexer = new Scanner()
-  return parser.parse(string)
+module.exports = function (source) {
+  return parse(scan(source))
 }