avoid LLVM warning: skip ternary operator when value is unsigned (-Wtautological-compare).

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extra : transplant_source : %87%E8%C9%0A%B8%1A%C34%26H%B8%0F%89%D4%8CC%10%1A%0F%84
add IPython notebook screenshot to the docs

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extra : transplant_source : -%C1%5B%21Igwr%87%0A%03%E7%D4%E8%A7%19%97%F1%D8p
shrink doc images
merge 0.21.x branch into master
merge
allow external 'cpdef cfunc' overrides in .pxd files
shrink Cython logo image files
prepare release of 0.21.1
changelog
Added tag 0.21.1 for changeset 58fc9a3feb83
extend "make clean"
Added tag 0.21.1 for changeset d05a4acd45fc
merge 0.21.x branch into master
changelog
fix compiler crash due to inconsistent method signature
disable refnanny in tests under PyPy
Allow cpdef void-returning functions.
do not create (potentially unused) C function coercion code when all we do is ask if it's possible
avoid some more accidental type coercion helper code generation
extend test