chore: add Travis CI docs deployment job and update build dependencies

- Add automatic docs deployment stage for master branch pushes in .travis.yml
- Include python3-markdown, python3-pygments, python3-setuptools, and ruby-sass as build dependencies
- Switch from container-based to sudo-required builds with trusty dist for custom Pygments lexer installation
- Ensure build directory exists before generating docs in Makefile

test/language/bom.wren

@@ -0,0 +1,2 @@
+// This file should have a UTF-8 byte order mark
+System.print("ok") // expect: ok

test/language/variable/many_locals.wren

@@ -1,6 +1,6 @@
 {
-  var a0 = "value"
-  var a1 = a0
+  // Slot zero is always taken to hold the closure or receiver.
+  var a1 = "value"
   var a2 = a1
   var a3 = a2
   var a4 = a3

test/language/variable/many_nonsimultaneous_locals.wren

@@ -1,10 +1,10 @@
-// Can have more than 256 local variables in a local scope, as long as they
+// Can have more than 255 local variables in a local scope, as long as they
 // aren't all in scope at the same time.
 
 {
   {
-    var a0 = "value a"
-    var a1 = a0
+    // Slot zero is always taken to hold the closure or receiver.
+    var a1 = "value a"
     var a2 = a1
     var a3 = a2
     var a4 = a3
@@ -263,8 +263,8 @@
   }
 
   {
-    var b0 = "value b"
-    var b1 = b0
+    // Slot zero is always taken to hold the closure or receiver.
+    var b1 = "value b"
     var b2 = b1
     var b3 = b2
     var b4 = b3

test/language/variable/too_many_locals.wren

@@ -1,6 +1,6 @@
 {
-  var a0 = "value"
-  var a1 = a0
+  // Slot zero is always taken to hold the closure or receiver.
+  var a1 = "value"
   var a2 = a1
   var a3 = a2
   var a4 = a3

test/language/variable/too_many_locals_nested.wren

@@ -1,6 +1,6 @@
 {
-  var a0 = "value"
-  var a1 = a0
+  // Slot zero is always taken to hold the closure or receiver.
+  var a1 = "value"
   var a2 = a1
   var a3 = a2
   var a4 = a3