.gitignore: ignore all built examples

docs/examples/.gitignore

+10-at-a-time
+anyauthput
+certinfo
+chkspeed
+cookie_interface
+debug
+fileupload
+fopen
+ftp-wildcard
+ftpget
+ftpgetinfo
+ftpgetresp
+ftpupload
+getinfo
+getinmemory
+http-post
+httpcustomheader
+httpput
+https
+multi-app
+multi-debugcallback
+multi-double
+multi-post
+multi-single
+persistant
+post-callback
+postit2
+sendrecv
+sepheaders
+simple
+simplepost
+simplessl