Deprecation warning due to invalid escape sequences in Python 3.8

Deprecation warnings are emitted in Python 3.8 for invalid escape sequences. Escaping them or using raw strings will fix this issue.

```
find . -iname '*.py' | xargs -P 4 -I{} python3.8 -Wall -m py_compile {}
./test/test_samplefile.py:41: DeprecationWarning: invalid escape sequence \s
offset = len(re.compile('(\s*)').match(lines[0]).group())
./test/test_samplefile.py:43: DeprecationWarning: invalid escape sequence \w
'[\w:]+)\])?(\s+linked to (?P[\w/]+))?')
./odml/rdf/query_creator.py:91: DeprecationWarning: invalid escape sequence \(
doc_pattern = re.compile("(doc|document)\(.*?\)")
./odml/rdf/query_creator.py:96: DeprecationWarning: invalid escape sequence \(
sec_pattern = re.compile("(sec|section)\(.*?\)")
./odml/rdf/query_creator.py:101: DeprecationWarning: invalid escape sequence \(
prop_pattern = re.compile("(prop|property)\(.*?\)")
./odml/rdf/query_creator.py:107: DeprecationWarning: invalid escape sequence \(
p = re.compile("[\(|, ](id|author|date|version|repository|sections)[\)|,]")
./odml/rdf/query_creator.py:112: DeprecationWarning: invalid escape sequence \(
p = re.compile("[\(|, ](id|name|definition|type|repository|reference|sections|properties)[\)|,]")
./odml/rdf/query_creator.py:117: DeprecationWarning: invalid escape sequence \(
p = re.compile("[\(|, ](id|name|definition|dtype|unit|uncertainty|reference|value_origin)[\)|,]")
./odml/rdf/query_creator.py:153: DeprecationWarning: invalid escape sequence \(
doc_pattern = re.compile("(doc|document)\(.*?\)")
./odml/rdf/query_creator.py:158: DeprecationWarning: invalid escape sequence \(
sec_pattern = re.compile("(sec|section)\(.*?\)")
./odml/rdf/query_creator.py:163: DeprecationWarning: invalid escape sequence \(
prop_pattern = re.compile("(prop|property)\(.*?\)")
./odml/rdf/query_creator.py:171: DeprecationWarning: invalid escape sequence \(
p = re.compile("[, |\(](id|author|date|version|repository|sections):(.*?)[,|\)]")
./odml/rdf/query_creator.py:176: DeprecationWarning: invalid escape sequence \(
p = re.compile("[, |\(](id|name|definition|type|repository|reference|sections|properties):(.*?)[,|\)]")
./odml/rdf/query_creator.py:181: DeprecationWarning: invalid escape sequence \(
p = re.compile("[, |\(](id|name|definition|dtype|unit|uncertainty|reference|value_origin):(.*?)[,|\)]")
./odml/rdf/query_creator.py:185: DeprecationWarning: invalid escape sequence \[
p_value = re.compile("value:\[(.*)]")
```