unix: check UV_CLOSING flag in uv__write()

uv__write() runs after the read callbacks have fired. Said callbacks may have
closed the handle, handle that graciously.
unix: fix warning: return 0 in function returning void
test: make test runner return non-zero in case of failure
test: add `.travis.yml` for testing on Travis CI
doc: add Travis CI build status image
Update AUTHORS and .mailmap
.gitignore core and vgcore files.
Fix missing increments of loop->counters
windows: fix memory leak when non-zero tcp reads are used
windows: correctly check the result of malloc
linux: improve kernel feature detection

Do not check for minimum kernel and glibc versions, just check that the kernel
headers export the syscall number and invoke the syscall directly. Effectively
bypasses glibc.
linux: detect if inotify syscalls are supported
unix: the dl functions don't set errno
unix: it's legal for dlsym() to return NULL

A symbol name can map to NULL. Check dlerror() to see if a real error happened.
docs: add c-ares license note
windows: ensure that uv_fs_event callbacks have long names
windows: uv_fs_rename to replace the new file if it exists
fixes #283
unix: unref fs event watcher

Watchers were being ref-counted twice which wasn't harmful in itself but stopped
uv_unref() from working like you'd expect it to.
linux: fix build on older distros
windows: improve uv_fs_stat performance (by about 60%)