Fix self arg type when adding optional arguments in an override.
fix typo in docs

--HG--
extra : rebase_source : 4cc5a2b5b9044e06fca82d216aa5a3c919abf033
minor doc clarification
fix typo in docs

--HG--
extra : rebase_source : 4cc5a2b5b9044e06fca82d216aa5a3c919abf033
minor doc clarification
Merge branch '0.20.x'
fix typo in docs

--HG--
extra : rebase_source : 4cc5a2b5b9044e06fca82d216aa5a3c919abf033
minor doc clarification
Merge branch '0.20.x'
optimise simple cases of adding string literals

--HG--
extra : transplant_source : w%8C%DC%3BS%CE%B2%8AC%D2%14%D3%99%B9%E8Z%0F%983%AD
fix syntax in test for old Py3 versions
capture C compiler output in test runner and discard it when expecting C compiler failures
move file descriptor redirecting to Cython.Utils package and use it as context manager in test runner
fix stderr test output printing in Py3
add helper for passing collected bytes output through to sys.stdout
make print_bytes() helper terminate output with line ending
use "cerror" tag instead of more verbose "_FAIL_C_COMPILE" special casing in test runner
another Py3 fix
improve presentation of C compiler stderr/stdout output in test runner
speed up Python object calculation of 2**N