Add Cairo snippet extractor (#108)

* Customing->customizing in README.md

* Add lib/languages/cairo.txt

* Add cairo tests

* Remove trailing newlines

* Remove whitespaces around comments

* Add other comment types

* Ignore mod keyword

* Revert HEAD

Author: 0xNeshi

Diff for: README.md

@@ -8,7 +8,7 @@ It takes the code of an Exercism submission and creates a snippet for it (shown
 ## Customizing snippet extraction
 
 By default, the snippet extractor extracts the first ten "interesting" (non-empty) lines of code.
-Whilst the default behavior is useful, we recommend customing snippet generation for most languages.
+Whilst the default behavior is useful, we recommend customizing snippet generation for most languages.
 
 ### Customization
 

Diff for: lib/languages/cairo.txt

@@ -0,0 +1,5 @@
+!e
+use
+//
+///
+//!

Diff for: tests/cairo/extended/code.cairo

@@ -0,0 +1,15 @@
+//! we will need this, trust me!
+use lib::some_function;
+
+// Hmmmmmmmm
+
+/// This comment is explaing
+/// a lot!!!
+mod two_fer { // we don't really
+    // have actual multiline
+    // comments!!
+    fn two_fer(name: ByteArray) -> ByteArray {
+        // There might be a comment here
+        return "One for " + name + ", one for me."; // A comment after a valid line 
+    }
+} // module two_fer

Diff for: tests/cairo/extended/expected_snippet.cairo

@@ -0,0 +1,5 @@
+mod two_fer {
+    fn two_fer(name: ByteArray) -> ByteArray {
+        return "One for " + name + ", one for me.";
+    }
+}

Diff for: tests/cairo/full/code.cairo

@@ -0,0 +1,7 @@
+use lib::some_function;
+
+mod two_fer {
+    fn two_fer(name: ByteArray) -> ByteArray {
+        return "One for " + name + ", one for me.";
+    }
+}

Diff for: tests/cairo/full/expected_snippet.cairo

@@ -0,0 +1,5 @@
+mod two_fer {
+    fn two_fer(name: ByteArray) -> ByteArray {
+        return "One for " + name + ", one for me.";
+    }
+}