winssl: be consistent in Schannel capitalization

The productname from Microsoft is "Schannel", but in infof/failf
reporting we use "schannel". This removes different versions.

Closes #3243
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

docs/HTTP2.md

@@ -7,7 +7,7 @@ HTTP/2 with curl
 Build prerequisites
 -------------------
   - nghttp2
-  - OpenSSL, libressl, BoringSSL, NSS, GnutTLS, mbedTLS, wolfSSL or SChannel
+  - OpenSSL, libressl, BoringSSL, NSS, GnutTLS, mbedTLS, wolfSSL or Schannel
     with a new enough version.
 
 [nghttp2](https://nghttp2.org/)
@@ -61,7 +61,7 @@ the necessary TLS features. Right now we support:
   - NSS:              ALPN and NPN
   - GnuTLS:           ALPN
   - mbedTLS:          ALPN
-  - SChannel:         ALPN
+  - Schannel:         ALPN
   - wolfSSL:          ALPN
   - Secure Transport: ALPN
 

docs/INSTALL.md

@@ -248,7 +248,7 @@ look for dynamic import symbols.
 
 ## Legacy Windows and SSL
 
-WinSSL (specifically SChannel from Windows SSPI), is the native SSL library in
+WinSSL (specifically Schannel from Windows SSPI), is the native SSL library in
 Windows. However, WinSSL in Windows <= XP is unable to connect to servers that
 no longer support the legacy handshakes and algorithms used by those
 versions. If you will be using curl in one of those earlier versions of

docs/KNOWN_BUGS

@@ -411,12 +411,12 @@ problems may have been fixed or changed somewhat since this was written!
 6.1 NTLM authentication and unicode
 
  NTLM authentication involving unicode user name or password only works
- properly if built with UNICODE defined together with the WinSSL/schannel
+ properly if built with UNICODE defined together with the WinSSL/Schannel
  backend. The original problem was mentioned in:
  https://curl.haxx.se/mail/lib-2009-10/0024.html
  https://curl.haxx.se/bug/view.cgi?id=896
 
- The WinSSL/schannel version verified to work as mentioned in
+ The WinSSL/Schannel version verified to work as mentioned in
  https://curl.haxx.se/mail/lib-2012-07/0073.html
 
 6.2 MIT Kerberos for Windows build

docs/libcurl/opts/CURLINFO_CERTINFO.3

@@ -71,8 +71,8 @@ if(curl) {
 }
 .fi
 .SH AVAILABILITY
-This option is only working in libcurl built with OpenSSL, NSS, schannel or
-GSKit support. schannel support added in 7.50.0
+This option is only working in libcurl built with OpenSSL, NSS, Schannel or
+GSKit support. Schannel support added in 7.50.0
 
 Added in 7.19.1
 .SH RETURN VALUE