Documentation out of date for Yubikey 5

[mdempsky]

Some documentation seems to be missing updates for Yubikey 5. Examples:

• https://developers.yubico.com/PIV/Introduction/Certificate_slots.html -- Mentions Yubikey 4 supports 20 "retired key management" certificate slots, and that "only" Yubikey 4 supports this. According to the Yubikey 5 Technical Manual, the Yubikey 5 supports these same slots. (On the other hand, this Yubikey 5 marketing page claims the PIV applet only "Supports twelve key slots on the YubiKey 5 Series keys(max per cert size of 3,052 bytes)".)

• https://developers.yubico.com/PIV/Introduction/YubiKey_and_PIV.html -- Mentions Yubikey 5, but only mentions RSA 1024, RSA 2048, and ECC secp256r1. The above technical manual and marketing page both also mention ECC P-384. The developers page mentions the maximum "stored object" size is 3049 bytes for Yubikey 4; https://www.yubico.com/solutions/smart-card/ mentions certificates can be up to 3052 bytes.