Add str.contains method

[Uwe L. Korn]

• ✔️ pandas function
• ✔️ Python function: in
• ✔️ C++ STL function
• ❌ needs a regular expression library
• ✔️ no need for a Unicode database (for case=True, otherwise need lower implementation)
• ✔️ can precompute output size as the result is a boolean array

Pseudo-Code:

Inputs: pat

output = BooleanArray(len(rows))

for i, row in enumerate(rows):
    output[i] = pat in row