printer: drop dependency on base64 crate

Instead, we just roll our own. A slow version of this is pretty simple
to do, and that's what we write here. The `base64` crate supports a lot
more functionality and is quite fast, but we care about neither of those
things for this particular aspect of ripgrep. (base64 is only used for
non-UTF-8 data or file paths, which are both quite rare.)

Cargo.lock

@@ -23,12 +23,6 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
 
-[[package]]
-name = "base64"
-version = "0.21.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9ba43ea6f343b788c8764558649e08df62f86c6ef251fdaeb1ffd010a9ae50a2"
-
 [[package]]
 name = "bstr"
 version = "1.7.0"
@@ -185,7 +179,6 @@ dependencies = [
 name = "grep-printer"
 version = "0.1.7"
 dependencies = [
- "base64",
  "bstr",
  "grep-matcher",
  "grep-regex",