Add strings.pyx demo

src/strings.pyx

+from stdlib.string cimport Str
+from libcythonplus.dict cimport cypdict
+from libcythonplus.list cimport cyplist
+from libc.stdio cimport puts, printf
+
+import traceback
+
+def test_hash():
+    with nogil:
+        s = Str('hello')
+        h = s.__hash__()
+        printf("hash('hello') = %lu\n", h)
+
+        d = cypdict[Str, int]()
+        d[Str('one')] = 1
+        d[Str('two')] = 2
+
+        one = d[Str('one')]
+        printf("one: %d\n", one)
+
+
+def test_split():
+    with nogil:
+        s = Str("Split this  sentence . ")
+        words = s.split()
+        for w in words:
+            puts(Str.to_c_str(w))
+
+        spaced = s.split(Str(' '))
+        for w in spaced:
+            puts(Str.to_c_str(w))
+
+
+def test_join():
+    with nogil:
+        delimiter = Str(", ")
+        elements = cyplist[Str]()
+        elements.append(Str("one"))
+        elements.append(Str("two"))
+        elements.append(Str("three"))
+        elements.append(Str("four"))
+        joined = delimiter.join(elements)
+        puts(Str.to_c_str(joined))
+
+
+def test_conversions():
+    with nogil:
+        number = Str('42')
+        integer = <int> number
+        printf('%s -> %d\n', Str.to_c_str(number), integer)
+
+        upper = Str('Hello-World')
+        lower = upper.lower()
+        printf("%s -> %s\n", Str.to_c_str(upper), Str.to_c_str(lower))
+
+        word = Str('word')
+        # C++ exception not handled if conversion operator is called implicitly
+        # fail = <int> word
+        fail = word.__int__()
+
+
+def main():
+    for f in (test_split, test_join, test_hash, test_conversions):
+        print(">>> %s()" % f.__name__)
+        try:
+            f()
+        except Exception:
+            traceback.print_exc()
+
+
+main()
+