Use bytesize to get content size

[tr4b4nt]

First of all thanks for this gem! We were really happy to find replacement for the abandoned azure-storage-blob.

After upgrading to this gem we started seeing weird 403 errors from time to time. The problem turned out to be with multi-byte UTF-8 characters and Content-Length header. Azure returns rather cryptic error when Content-Length header does not match actual length of the content (the error is included at the end).

Here is simple code to reproduce the problem:

client = AzureBlob::Client.new(...)
client.create_append_blob "test"
client.append_blob_block "test", "Ň"

Redacted Azure error response:

<Error><Code>AuthenticationFailed</Code><Message>Server failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature.</Message><AuthenticationErrorDetail>The MAC signature found in the HTTP request 'xxx' is not th
e same as any computed signature. Server used following string to sign: 'xxx'.</AuthenticationErrorDetail></Error>

[JoeDupuis]

Nice catch! Thank you for opening the PR.
There is a small issue. But everything else looks good!

[JoeDupuis]

This will break for StringIO.

Here's what Microsoft did on the old gem:
https://github.com/Azure/azure-storage-ruby/blob/master/common/lib/azure/core/auth/shared_key.rb#L62-L66

Suggested change

	def content_size(content)
	content.bytesize
	end
	def content_size(content)
	if content.respond_to?(:bytesize)
	content.bytesize
	else
	content.size
	end
	end

[tr4b4nt]

Thanks for the pointer. Fixed