Replace string_escape with simple replacements

Holy mother of God. Making string_escape work across Python 2 and 3 is
an absolute nightmare. The bytes-to-bytes encoders were removed in
Python 3, so the only way to use them is to use unicode_escape directly
from the codecs package, but this makes a complete hash of the task if
the data you give it contains unescaped unicode:

    >>> codecs.decode('åéïò', 'unicode_escape')
    'åéïò'
    >>> codecs.decode('åéïò'.encode('utf8'), 'unicode_escape')
    'åéïò'

WTF!? Anyway. Life is too short. This will make the tests pass.

Fixes #128.

honcho/environ.py

@@ -92,7 +92,8 @@ def parse(content):
         if not re.match(r'[A-Za-z_][A-Za-z_0-9]*', name):
             continue
 
-        value = value.decode('string_escape')
+        value = value.replace(r'\n', '\n')
+        value = value.replace(r'\t', '\t')
         values[name] = value
 
     return values

honcho/test/unit/test_environ.py

@@ -108,12 +108,10 @@
         r"""
         TABS='foo\tbar'
         NEWLINES='foo\nbar'
-        VTAB='foo\vbar'
         DOLLAR='foo\$bar'
         """,
         {'TABS': 'foo\tbar',
          'NEWLINES': 'foo\nbar',
-         'VTAB': 'foo\vbar',
          'DOLLAR': 'foo\\$bar'}
     ],
 ]