* Support self signed certificates
Fix for https://github.com/espressif/arduino-esp32/issues/265
mbedtls_ssl_conf_authmode was defined before mbedtls_ssl_config_defaults causing several bugs when no CA certificate is defined.
* Implement Arduino's log facility
Replace printf by ESP log handling
* Remove \n from debug messages
log_ doesn't need \n to break line.
* Add CA certificate in example
SHA1 fingerprint is broken now: more info: https://shattered.io
* Best error handling
When occur an error in WiFiClientSecure library just return the error message
and clean the context avoiding crash - fix for https://github.com/espressif/arduino-esp32/issues/211
Translate MbedTLS error codes in messages for best understanding
* Declarate certificates as const
mbedtls_pk_parse_key needs a const unsigned char * certificate. In old implementation the certificate was declarated as char * so first it converts to unsigned and after to const.
When we convert signed to unsigned it may result in a +1 larger output.
Fix issue https://github.com/espressif/arduino-esp32/issues/223
