Clean up the openssl "vendored" feature mess

The cleaner way is to take advantage of the single-dependency-deep
"slashed features" support in Cargo.toml to set features of direct
dependencies (not affecting recursive depnedencies) as implemented in
rust-lang/cargo#712

Cargo.toml

@@ -13,12 +13,11 @@ license = "MIT"
 edition = "2018"
 
 [dependencies]
-openssl = { version = "0.10", features = [ "vendored" ], optional = true }
-openssl-sys = { package = "openssl", version = "0.10", optional = true }
+openssl = { version = "0.10" }
 
 [features]
-default = [ "openssl" ]
-system-openssl = [ "openssl-sys" ]
+default = [ "openssl-vendored" ]
+openssl-vendored = [ "openssl/vendored" ]
 
 [dev-dependencies]
 base64 = "0.9"

examples/read.rs

@@ -1,6 +1,6 @@
 use base64::decode;
 use cryptostream::read;
-use cryptostream::Cipher;
+use openssl::symm::Cipher;
 use std::io::Read;
 
 fn main() {

examples/readme.rs

@@ -1,7 +1,6 @@
 use base64::decode;
 use cryptostream::{read, write};
-// openssl::Cipher is re-exported as cryptostream::Cipher
-use cryptostream::Cipher;
+use openssl::symm::Cipher;
 use std::io::prelude::*;
 
 fn main() {

examples/write.rs

@@ -1,6 +1,6 @@
 use base64::decode;
 use cryptostream::write;
-use cryptostream::Cipher;
+use openssl::symm::Cipher;
 use std::io::Write;
 
 fn main() {

src/lib.rs

@@ -29,22 +29,9 @@
 //! [`bufread::Decryptor`] types for encrypting/decrypting plaintext/ciphertext on-the-fly from a
 //! [`BufRead`](std::io::BufRead) source. (There is no need for a `bufwrite` variant.)
 
-#[cfg(not(feature = "system-openssl"))]
-extern crate openssl;
-#[cfg(feature = "system-openssl")]
-extern crate openssl_sys as openssl;
-
 pub mod bufread;
 pub mod read;
 pub mod write;
 
-/// Because we rename the openssl crate without the `vendored` feature as openssl_sys (you cannot
-/// have a dependency imported (even XOR conditionally) twice with the same name, and you cannot
-/// have conditional features for dependencies based off of your own feature in Cargo.toml), we
-/// re-export the `openssl::symm:Cipher` as `cryptostream::Cipher` so no `extern crate openssl` is
-/// required for downstream users of this library, which won't work if the `system-openssl` option
-/// were used.
-pub use openssl::symm::Cipher as Cipher;
-
 #[cfg(test)]
 mod tests;