Update release instructions for new robots.txt file
fix to preserve input image shape upon executing `random_walker`
PEP8 fixes; remove unneeded pyamg import; add `data` shape check
Use `force_copy` argument of `img_as_float`

Also three PEP8 fixes
Make return type of skeletonize function boolean
Reformat code to comply with PEP8
Remove unnecessary conversion step to numpy array
Remove duplicate import statement
Merge pull request #501 from ahojnnes/skeletonize

BUG: Fix `skeletonize` return type.
fix: remove unnecessary forced copy
add assertion checks to ensure `data` shape is unchanged
Merge pull request #500 from JDWarner/fix_preserve_rw_input_shape

BUG: Preserve input image shape upon executing `random_walker`.
Merge pull request #503 from ahojnnes/exposure

STY: Remove duplicate import statement.
Merge pull request #494 from ahojnnes/release-instr

DOC: Update release instructions for new robots.txt file.