fix bug unescaped_string_literal

Running the command:

erlydtl:compile(<<"{{ text|add:\"\\\"\" }}">>, test).

will result in a crash. string:strip will remove all \" from the
beginning and end of the string \"\\\"\", leaving only \\. It should
only remove one \" from the beginning of the string and one from the end.
change erlydtl filters handle unicode input
Merge branch 'bug-fix-escape-quotes' of https://github.com/campanja/erlydtl into campanja-bug-fix-escape-quotes

Conflicts:
	src/erlydtl_compiler.erl
	src/erlydtl_filters.erl
Fix broken truncate filters (#138)

```erlang
erlydtl_tests: all_defs_test_ (filters: |truncatewords:0)...*failed*
in function erlydtl_eunit_testrunner:'-run_render/1-fun-0-'/2 (test/erlydtl_eunit_testrunner.erl, line 73)
**error:{assertEqual_failed,[{module,erlydtl_eunit_testrunner},
                     {line,73},
                     {expression,"B"},
                     {expected,<<" ...">>},
                     {value,<<>>}]}
```
Add failing test for string quote fix in #138
Merge branch 'campanja-bug-fix-escape-quotes'