optimize: make it compatible with boringssl. (#28)

doc: updated the copyright years.

feature: added support for OpenSSL 1.1.0.

EVP_CIPHER_CTX is opaque after OpenSSL 1.1.0.
Replace EVP_CIPHER_CTX_init and EVP_CIPHER_CTX_cleanup with
EVP_CIPHER_CTX_new and EVP_CIPHER_CTX_free.

Signed-off-by: Yichun Zhang (agentzh) <agentzh@gmail.com>

doc: we now work with nginx cores as new as 1.13.6.

doc: this module works with nginx 1.11.x as far as 1.11.2.

doc: now we work with nginx cores as far as 1.9.15.

doc: switched to the markdown format; also added more detailed docume…

…ntation.

updated .gitignore to reflect recent changes.

fixed source lines exceeding 80 cols and also updated README to refle…

…ct recent changes.

fixed a nasty bug found by the no-pool-nginx patch combined with valg…

…rind :D