* 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
