Allow options to be passed for the spawned git process

Closes #1

Author: bendrucker

README.md

@@ -11,10 +11,12 @@ $ npm install git-log-parser
 
 ## API
 
-#### `log.parse(config)` -> `Stream(commits)`
+#### `log.parse(config, options)` -> `Stream(commits)`
 
 Accepts a `config` object mapping to the [options accepted by `git log`](http://git-scm.com/docs/git-log). `config` will be automatically converted to command line options and flags by [argv-formatter](https://github.com/bendrucker/argv-formatter). Returns a stream of commit objects. 
 
+`options` is passed directly to [`child_process.spawn`](https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options).
+
 A commit is structured as follows:
 
 ```js

src/index.js

@@ -30,8 +30,8 @@ function trim () {
   });
 }
 
-function log (args) {
-  return fwd(spawn('git', ['log'].concat(args)), function (code, stderr) {
+function log (args, options) {
+  return fwd(spawn('git', ['log'].concat(args), options), function (code, stderr) {
     return new Error('git log failed:\n\n' + stderr);
   })
   .stdout;
@@ -42,11 +42,11 @@ function args (config, fieldMap) {
   return toArgv(config);
 }
 
-exports.parse = function parseLogStream (config) {
+exports.parse = function parseLogStream (config, options) {
   config  = config || {};
   var map = fields.map();
   return combine([
-    log(args(config, map)),
+    log(args(config, map), options),
     split(END + '\n'),
     trim(),
     through.obj(function (chunk, enc, callback) {