tidy-up: OS names

Use these words and casing more consistently across text, comments and
one curl tool output:
AIX, ALPN, ANSI, BSD, Cygwin, Darwin, FreeBSD, GitHub, HP-UX, Linux,
macOS, MS-DOS, MSYS, MinGW, NTLM, POSIX, Solaris, UNIX, Unix, Unicode,
WINE, WebDAV, Win32, winbind, WinIDN, Windows, Windows CE, Winsock.

Mostly OS names and a few more.

Also a couple of other minor text fixups.

Closes #14360

docs/cmdline-opts/_ENVIRONMENT.md

@@ -87,7 +87,7 @@ names named after the destination connection id (in hex). Do note that these
 files can become rather large. Works with the ngtcp2 and quiche QUIC backends.
 
 ## `SHELL`
-Used on VMS when trying to detect if using a **DCL** or a **unix** shell.
+Used on VMS when trying to detect if using a **DCL** or a **Unix** shell.
 
 ## `SSL_CERT_DIR` <dir>
 If set, it is used as the --capath value. This environment variable is ignored

docs/cmdline-opts/cacert.md

@@ -27,7 +27,7 @@ curl recognizes the environment variable named 'CURL_CA_BUNDLE' if it is set
 and the TLS backend is not Schannel, and uses the given path as a path to a CA
 cert bundle. This option overrides that variable.
 
-The windows version of curl automatically looks for a CA certs file named
+The Windows version of curl automatically looks for a CA certs file named
 'curl-ca-bundle.crt', either in the same directory as curl.exe, or in the
 Current Working Directory, or in any folder along your PATH.
 

docs/cmdline-opts/create-dirs.md

@@ -21,6 +21,6 @@ mentioned with the --output option combined with the path possibly set with
 --output-dir. If the combined output filename uses no directory, or if the
 directories it mentions already exist, no directories are created.
 
-Created directories are made with mode 0750 on unix style file systems.
+Created directories are made with mode 0750 on Unix-style file systems.
 
 To create remote directories when using FTP or SFTP, try --ftp-create-dirs.

docs/cmdline-opts/false-start.md

@@ -20,4 +20,4 @@ client starts sending application data before verifying the server's Finished
 message, thus saving a round trip when performing a full handshake.
 
 This functionality is currently only implemented in the Secure Transport (on
-iOS 7.0 or later, or OS X 10.9 or later) backend.
+iOS 7.0 or later, or macOS 10.9 or later) backend.

docs/cmdline-opts/socks4.md

@@ -21,7 +21,7 @@ Use the specified SOCKS4 proxy. If the port number is not specified, it is
 assumed at port 1080. Using this socket type make curl resolve the hostname
 and passing the address on to the proxy.
 
-To specify proxy on a unix domain socket, use localhost for host, e.g.
+To specify proxy on a Unix domain socket, use localhost for host, e.g.
 `socks4://localhost/path/to/socket.sock`
 
 This option overrides any previous use of --proxy, as they are mutually

docs/cmdline-opts/socks4a.md

@@ -20,7 +20,7 @@ Example:
 Use the specified SOCKS4a proxy. If the port number is not specified, it is
 assumed at port 1080. This asks the proxy to resolve the hostname.
 
-To specify proxy on a unix domain socket, use localhost for host, e.g.
+To specify proxy on a Unix domain socket, use localhost for host, e.g.
 `socks4a://localhost/path/to/socket.sock`
 
 This option overrides any previous use of --proxy, as they are mutually

docs/cmdline-opts/socks5-hostname.md

@@ -19,7 +19,7 @@ Example:
 Use the specified SOCKS5 proxy (and let the proxy resolve the hostname). If
 the port number is not specified, it is assumed at port 1080.
 
-To specify proxy on a unix domain socket, use localhost for host, e.g.
+To specify proxy on a Unix domain socket, use localhost for host, e.g.
 `socks5h://localhost/path/to/socket.sock`
 
 This option overrides any previous use of --proxy, as they are mutually

docs/cmdline-opts/socks5.md

@@ -19,7 +19,7 @@ Example:
 Use the specified SOCKS5 proxy - but resolve the hostname locally. If the
 port number is not specified, it is assumed at port 1080.
 
-To specify proxy on a unix domain socket, use localhost for host, e.g.
+To specify proxy on a Unix domain socket, use localhost for host, e.g.
 `socks5://localhost/path/to/socket.sock`
 
 This option overrides any previous use of --proxy, as they are mutually

docs/cmdline-opts/use-ascii.md

@@ -19,4 +19,4 @@ Example:
 
 Enable ASCII transfer mode. For FTP, this can also be enforced by using a URL
 that ends with `;type=A`. This option causes data sent to stdout to be in text
-mode for win32 systems.
+mode for Win32 systems.