bump: start working on the next release
email: Renamed *_perform_authenticate() functions

In preparation for the upcoming SASL downgrade feature renamed the
imap__perform_authenticate(), pop3__perform_authenticate() and
smtp__perform_authenticate() functions.
imap: Moved the sending of the AUTHENICATE command into a separate function
pop3: Moved the sending of the AUTH command into a separate function
smtp: Moved the sending of the AUTH command into a separate function
imap: Moved the calculation of SASL login details into a separate function
pop3: Moved the calculation of SASL login details into a separate function
smtp: Moved the calculation of SASL login details into a separate function
smtp: fix compiler warning

smtp.c:478:21: error: unused variable 'smtpc' [-Werror=unused-variable]
gitignore: ignore .dirstamp files
RELEASE-PROCEDURE: new document
imap/pop3/smtp: Added support for SASL authentication downgrades

Added support for downgrading the SASL authentication mechanism when the
decoding of CRAM-MD5, DIGEST-MD5 and NTLM messages fails. This enhances
the previously added support for graceful cancellation by allowing the
client to retry a lesser SASL mechanism such as LOGIN or PLAIN, or even
APOP / clear text (in the case of POP3 and IMAP) when supported by the
server.
curl.1: remove URL encoding phrase from --data description

... it could be misleading a reader into thinking it _has_ to be encoded.
curl_easy_setopt: Fixed OAuth 2.0 Bearer option name

Bug: http://curl.haxx.se/bug/view.cgi?id=1313
Reported-by: Viktor Szakáts
pop3: Moved APOP detection into pop3_state_servergreet_resp()

In an effort to reduce what pop3_endofresp() does and bring the POP3
source back inline with the IMAP and SMTP protocols, moved the APOP
detection into pop3_state_servergreet_resp().
pop3: Moved CAPA response handling to pop3_state_capa_resp()

Similar to the processing of untagged CAPABILITY responses in IMAP and
multi-line EHLO responses in SMTP, moved the processing of multi-line
CAPA responses to pop3_state_capa_resp().
pop3: Fixed processing of more than one response when sent in same packet

Added a loop to pop3_statemach_act() in which Curl_pp_readresp() is
called until the cache is drained. Without this multiple responses
received in a single packet could result in a hang or delay.
pop3: Fixed selection of APOP when server replies with an invalid timestamp

Although highlighted by a bug in commit 1cfb436a2f1795, APOP
authentication could be chosen if the server was to reply with an empty
or missing timestamp in the server greeting and APOP was given in the
capability list by the server.
vtls: created subdir, moved sslgen.[ch] there, updated all include lines
vtls: moved all TLS/SSL source and header files into subdir