Created Tutorial: Hacking the Nimrod compiler: Pragmas (markdown)

Tutorial:-Hacking-the-Nimrod-compiler:-Pragmas.md

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+## Introduction
+As there are no tutorials (that I know of) on how to add new features to the nimrod
+compiler I have decided to make one, based on me implementing the `requires`
+pragma which will be used for Babel Packages.
+
+As with many tasks there are many tools that are very helpful, I have used
+the *nimgrep* tool which is in the tools/ directory in Nimrod's repository, but I'm sure you know of other tools which can be very helpful!
+
+## First steps
+The first thing I have decided to do was create a test file, it follows:
+
+    {.requires packageA "0.7" "0.9".}
+    echo("hi")
+  
+(It originally had a `..` between the two string literals, I decided to get rid
+of that because I noticed that pragmas don't support it, I might come back to it.)
+
+I then saved that file as *"pragmaTest.nim"* and compiled it with
+`nimrod c pragmaTest.nim`. This has caused `pragmaTest.nim(1, 10) Error: invalid pragma: requires`.
+
+The next step was quite obvious, searching for "invalid pragma:", `nimgrep --recursive --ext:nim "invalid\ pragma:"`,
+this only gives one result.
+
+    ../Nimrod/rod/msgs.nim
+      258:     errInvalidPragmaX: "invalid pragma: $1",
+
+After some more intellectual grepping and looking through files, I noticed that the pragma() function in pragmas.nim
+takes an argument called `validPragmas` this lead me to *semtypes.nim* and *semstmts.nim* 
+after searching for (yes, you've guessed it) `pragma(`(please note this needs escaping when used as a regex).
+
+There was many `pragma` calls, I have looked at most of them and since I wanted
+a "global"(not sure if that's the correct term) pragma, for example
+`{.warning: "warning".}`. The `pragma` function is called with many different
+valid pragma groups. There is among many others, `stmtPragmas`, which is what
+I wanted, it's defined in *pragmas.nim*.
+
+## Hacking the code!
+I found where `TSpecialWords` is defined(*wordrecg.nim*) and added `wRequires`
+there, to the `specialWords` array below, and also to `stmtPragmas`. I then added `wRequires` to the case statement in the `pragma` function in *pragmas.nim*.
+
+This is where the `debug` function came into play, it is a function that pretty prints a 
+node in the AST, it is very useful. I added two `debug` calls one for the 'it' node
+and another one for the 'n' node.
+
+I then bootstrapped by executing `./koch boot`. After I got the beautiful "SUCCESS",
+I compiled *pragmaTest.nim*. And I got this output: 
+
+    {
+      "kind": "nkIdent",
+      "ident": "requires"
+    }
+    {
+      "kind": "nkPragma",
+      "sons": [
+        {
+          "kind": "nkIdent",
+          "ident": "requires"
+        },
+        {
+          "kind": "nkIdent",
+          "ident": "packageA"
+        },
+        {
+          "kind": "nkStrLit",
+          "strVal": "0.7"
+        },
+        {
+          "kind": "nkStrLit",
+          "strVal": "0.9"
+        }
+      ]
+    }
+