Update bip-0070.mediawiki

Slightly re-worded description of the signature field in PaymentRequest

The previous phrasing confused me and I had to check the Bitcoin Core source code to see what it was expecting for a signature.
Define a deadline for returning funds via refund_to.

See discussion "BIP 70 refund field" on bitcoin-dev.
Require including intermediate certificates in a BIP70 payment request.
Update bip-0038.mediawiki

Fix some erroneous statements in the description of the math used for encryption/decryption of EC-Multiplied keys/addresses
Add test case for UTF8 NFC normalization
Add normalization note on test case
Attempt to put the actual characters in the source file
Replaced example domain name with example.com.
Added file size limits for Payment and PaymentACK messages.
Added note about handling multiple copies of a Payment message, to ensure resend is safe
in case of a transport layer failure.
Added reference to RFC 2616 to BIP0072.
Added note about handling HTTP statuses which are neither error nor success.
Expanded and clarified wording on recovering from error states when sending payment to the merchant's server.
Update bip-0070.mediawiki

Change "zero-byte placeholder" to "empty string"
fix typos in BIP-0043 and BIP-0044
Loosened URL validity period on payment requests.
Update bip-0070.mediawiki

Revised final sentence of signature field description.
Minor grammatical & spelling corrections
C# implementation

Github link to a C# implementation
Small typo