Fix constant folding of multiplied string literals when they appear in another constant expression. In this case, the multiplied value was lost and replaced by the original value.

cython_inline compiler directives support

Support two-element slicing with literal None

Closes #2587.

Simplify encoding detection and source file opening by starting off reading bytes, and only switching to decoding once we know which encoding to use.

Further experimentation - leaks references, C compilation raises warnings, C++ compilation fails outright.

Reworking slicing unittests to include sliced type - added unsuccessful attempt to resolve issue #2508.