Added support for imports and many other .proto features.

Change-Id: I6600021b7ec8c486794349511232c3e604421c5b
Tested: on Linux.

tests/prototest/imported.proto

@@ -0,0 +1,5 @@
+package proto.test;
+
+message ImportedMessage {
+    optional int32 a = 26;
+}

tests/prototest/test.golden

@@ -1,14 +1,22 @@
 // Generated from test.proto
 
-namespace proto.test;
+namespace _proto._test;
 
 /// Enum doc comment.
-enum ProtoEnum : short {
+enum ProtoEnum : int {
   FOO = 1,
   /// Enum 2nd value doc comment misaligned.
   BAR = 5,
 }
 
+namespace _proto._test;
+
+table ImportedMessage {
+  a:int;
+}
+
+namespace _proto._test;
+
 /// 2nd table doc comment with
 /// many lines.
 table ProtoMessage {
@@ -29,10 +37,13 @@ table ProtoMessage {
   /// lines
   l:string (required);
   m:string;
-  n:OtherMessage;
+  n:_proto._test._ProtoMessage.OtherMessage;
   o:[string];
+  z:_proto._test.ImportedMessage;
 }
 
+namespace _proto._test._ProtoMessage;
+
 table OtherMessage {
   a:double;
   /// doc comment for b.

tests/prototest/test.proto

@@ -1,9 +1,9 @@
 // Sample .proto file that we can translate to the corresponding .fbs.
 
-package proto.test;
-
 option some_option = is_ignored;
-import "some_other_schema.proto";
+import "imported.proto";
+
+package proto.test;
 
 /// Enum doc comment.
 enum ProtoEnum {
@@ -41,4 +41,5 @@ message ProtoMessage {
   optional bytes m = 11;
   optional OtherMessage n = 12;
   repeated string o = 14;
+  optional ImportedMessage z = 16;
 }