Auto merge of #3684 - casey:search-copy-pastafication, r=alexcrichton

Increase copypastafication of `cargo search`

Formats the search results printed by `cargo search` so that they can be
copied directly into a `Cargo.toml` file.

I used `^`, since I like being explicit, although that seems not to be the convention, so I'd be happy to remote it.

I also added a `#` in front of the description, so that that can be copy pastaed as well. I'm not super attached to this idea, but I think it's interesting, since it would serve to document what the various dependencies of a crate are for new contributors.

For example:

```
$ cargo search clap
clap = "^2.20.3"               # A simple to use, efficient, and full featured  Command Line ArgumentParser
please-clap = "^0.1.0"         # Pattern-match against Clap subcommands and arguments.
clapcomp = "^0.1.5"            # clap completion generator as command
clap-test = "^0.1.1"           # functions and macros to assist in testing clap
structopt = "^0.0.2"           # Parse command line argument by defining a struct.
capgun = "^0.1.1"              # fire when ready file watcher
structopt-derive = "^0.0.2"    # Parse command line argument by defining a struct, derive crate.
cargo-outdated = "^0.3.0"      # Cargo subcommand for displaying when dependencies are out of date
wesers = "^0.4.1"              # a simple HTTP/HTTPS server in Rust
cargo-arch = "^0.1.0"          # Rust Arch Linux package packer
... and 6 crates more (use --limit N to see more)
```