shareonline.biz: add probe support

Thanks to stefan.111.meier
plow*: explicitly check for module function

Could prevent typo in module or bad module/config file.
plowdown: add two user-friendly checks

- when no output directory specified, check if $PWD is writable
- check if provided url can be used with plowlist
billionuploads: add anonymous upload
billionuploads: add probe support
180upload (upload): use curl's --form-string (instead of -F) to prevent $DESCRIPTION being interpreted
cloudzer_net: initial module with anonymous download

Original patch provided by stefan.111.meier
rapidgator (download): put 15 minutes interval between two rapidgator links
turbobit (upload, login): fix, upstream modified

- fix upload procedure
- add account type detection to "login"
core.sh (basename_url): use bash regular expressions instead of sed
docs (plowdown.1): cosmetics (missing point)
plow*: explicitly check for module function

Could prevent typo in module or bad module/config file.
mediafire (list): fix, use API, support sub folders
euroshare.eu: fix anonymous download & upload (upstream modified)