Improved tests

Hi,

While working on the new scanner, I needed a more stable test environment.
So I have cherry-pick'ed out those commits here, as the new scanner has come to a halt, for now.
(the incomplete work, in a non-workable state, is in my `new_scanner` branch).

Some example snippets of output (from my scrollback history) of both error and success examples:
```
 Template: "ifnotequal_preset", ... compiling ... rendering ... ok
 Template: "now", ... compiling ... rendering ... ok (not checked for regression)
 Template: "var", ... compiling ... rendering ... ok
...
All 33 functional tests passed
...
Unit test failures: 0
---
 Test group "contrib_humanize"...
 Test group "extension_module"...
Unit test failures: 1
  extension_module:replace parsed token 
    error:undef
    [{erlydtl_scanner,next,
         [{scanner_state,"# }}",
              {1,8},
              [{identifier,{1,4},bar},{open_var,{1,1},'{{'}],
              [{scope,6,8,
                   {tag,code,text,10,"{{","}}",
                       [reverse_string,{open_var,'{{'}],
----
 Template: "autoescape", ... compiling ... failed
 Template: "comment", ... compiling ... failed
 Template: "extends", ... compiling ... 
 Template: "filters", ... compiling ... rendering ... ok
 Template: "for", ... compiling ... 
 Template: "for_list", ... compiling ... 
 Template: "for_tuple", ... compiling ... 
 Template: "for_list_preset", ... compiling ... 
 Template: "for_preset", ... compiling ... failed
 Template: "for_records", ... compiling ... 
 Template: "for_records_preset", ... compiling ... failed
 Template: "include", ... compiling ... rendering ... ok
...
 Template: "trans", ... compiling ... rendering ... ok
17 / 33 functional tests failed.
Errors: 
  extends_path [crash] {function_clause,
    [{erlydtl_scanner,move,
         [83,
          {scanner_state,[],
...
  include_path [crash] {function_clause,
    [{erlydtl_scanner,move,
         [110,
          {scanner_state,[],
              {6,1},
              [{open_var,{5,2},'{{'},
...
  custom_call [crash] {undef,
    [{example_for_preset,dependencies,[],[]},
     {erlydtl_compiler,call_ast,4,
         [{file,"src/erlydtl_compiler.erl"},{line,1512}]},
     {lists,mapfoldl,3,[{file,"lists.erl"},{line,1278}]},
...
  cycle [crash] {function_clause,
    [{erlydtl_scanner,move,
         [43,
          {scanner_state,[],
              {10,1},
              [{open_var,{5,6},'{{'},
...
```