Code style: Make all static "require" calls global

The "global-require" rule is disabled in ESLint configuration used by
PEG.js, but the idea is not bad, so let's make all static "require"
calls global.

Follow-up to #407.

lib/compiler/index.js

@@ -1,5 +1,15 @@
 "use strict";
 
+let generateBytecode = require("./passes/generate-bytecode");
+let generateJS = require("./passes/generate-js");
+let removeProxyRules = require("./passes/remove-proxy-rules");
+let reportDuplicateLabels = require("./passes/report-duplicate-labels");
+let reportDuplicateRules = require("./passes/report-duplicate-rules");
+let reportInfiniteRecursion = require("./passes/report-infinite-recursion");
+let reportInfiniteRepetition = require("./passes/report-infinite-repetition");
+let reportUndefinedRules = require("./passes/report-undefined-rules");
+let visitor = require("./visitor");
+
 function processOptions(options, defaults) {
   let processedOptions = {};
 
@@ -19,7 +29,7 @@ function processOptions(options, defaults) {
 let compiler = {
   // AST node visitor builder. Useful mainly for plugins which manipulate the
   // AST.
-  visitor: require("./visitor"),
+  visitor: visitor,
 
   // Compiler passes.
   //
@@ -28,18 +38,18 @@ let compiler = {
   // |peg.GrammarError|.
   passes: {
     check: {
-      reportUndefinedRules: require("./passes/report-undefined-rules"),
-      reportDuplicateRules: require("./passes/report-duplicate-rules"),
-      reportDuplicateLabels: require("./passes/report-duplicate-labels"),
-      reportInfiniteRecursion: require("./passes/report-infinite-recursion"),
-      reportInfiniteRepetition: require("./passes/report-infinite-repetition")
+      reportUndefinedRules: reportUndefinedRules,
+      reportDuplicateRules: reportDuplicateRules,
+      reportDuplicateLabels: reportDuplicateLabels,
+      reportInfiniteRecursion: reportInfiniteRecursion,
+      reportInfiniteRepetition: reportInfiniteRepetition
     },
     transform: {
-      removeProxyRules: require("./passes/remove-proxy-rules")
+      removeProxyRules: removeProxyRules
     },
     generate: {
-      generateBytecode: require("./passes/generate-bytecode"),
-      generateJS: require("./passes/generate-js")
+      generateBytecode: generateBytecode,
+      generateJS: generateJS
     }
   },
 

lib/peg.js

@@ -1,12 +1,16 @@
 "use strict";
 
+let GrammarError = require("./grammar-error");
+let compiler = require("./compiler");
+let parser = require("./parser");
+
 let peg = {
   // PEG.js version (uses semantic versioning).
   VERSION: "0.10.0",
 
-  GrammarError: require("./grammar-error"),
-  parser: require("./parser"),
-  compiler: require("./compiler"),
+  GrammarError: GrammarError,
+  parser: parser,
+  compiler: compiler,
 
   // Generates a parser from a specified grammar and returns it.
   //