correct faulty comments in thread_first/last

Thanks to @eriknw for finding this error

Fixes #54
add link to github from toolz main page

Fixes #55

Suggested by @eigenhombre
refer to python functional programming doc page
rename argument f -> binop in accumulate
Merge pull request #51 from mrocklin/pipe

add pipe function
add key keyword argument to merge
Merge accepts iterable of dicts

Fixes #50
rename merge key to func