Renamed package 'greg' to 'regex'

regex/todo.txt

@@ -0,0 +1,7 @@
+1. Error-checking - invalid regex, Out-of-bounds stuff. Do more testing.
+2. More features - Non-greedy operators, backreferences, non-capturing groups, escaped characters inside character classes
+3. Fix adding concatenation operators in shunting-yard function (very janky, compares against operators individually)
+Ideas for flags:
+    -m <num> : Print <num>th match (-m 1 = first match, -m 2 = second match)
+    -g <num> : Print the <num>th group
+4. Refactor code for flags - make each flag's code a function, which modifies the result of findAllMatches