Adding tests for "Unicode and passing strings" part 6

docs: Give the string input conversion function in the string tutorial a better name and clarify some comments.

Adding tests for "Unicode and passing strings" part 5

Adding tests for "Unicode and passing strings" part 3

Adding tests for "Unicode and passing strings" part 2

Adding tests for "pure python mode" part 11

Adding tests for "pure python mode" part 10

Adding tests for "pure python mode" part 9

Adding tests for "pure python mode" part 8

Adding tests for "Basic tutorial"

Added tests to "Using Parallelism" part 1

Added tests to "Memoryviews" part 1

Added tests to "Fused types (templates)" part 1

Added tests to "Interfacing with external C code" part 1

Added tests to "Implementing the buffer protocol" part 1

See #2362.

Enhance "wrapping C libraries".

Added tests to "Early binding for speed" part 1

Extended the examples of string.rst and put them in the examples directory for testing.

Added tests to "Extension types" part 1