syntax: 'var'->'let' 'function'->'func'

- 'var' has some weird scoping connotations with users of JS. better to change it to 'let', which will decide whether to make the variable a local or a global
- 'func' looks visually appealing lol
- some minor refactoring done in cparse.c

examples/strings.cosmo

@@ -1,7 +1,7 @@
-var words = "hello world! this is a sentence with words separated by space":split(" ")
+let words = "hello world! this is a sentence with words separated by space":split(" ")
 
-var str = ""
-for (var i = 0; i < #words; i++) do
+let str = ""
+for (let i = 0; i < #words; i++) do
     str = str .. words[i]
     print(words[i])
 end