Migrate to csv crate rewrite.0.12.0

This commit resists the urge to refactor/rewrite xsv and ports it over
to the new CSV API. It made a lot of things cleaner and even improved
the performance of core commands like `count`, `sample`, `search`,
`select` and `slice`.

This also removes the last remaining (dubious) uses of `unsafe` within
xsv.

Benchmarks before/after:

    benchmark               before                      after
    count                   0.26s   175.05  MB/sec      0.11   413.76  MB/sec
    flatten                 4.53s   10.04   MB/sec      4.54   10.02   MB/sec
    flatten_condensed       4.72s   9.64    MB/sec      4.45   10.22   MB/sec
    frequency               1.91s   23.82   MB/sec      1.82   25.00   MB/sec
    index                   0.28s   162.54  MB/sec      0.12   379.28  MB/sec
    sample_10               0.43s   105.84  MB/sec      0.18   252.85  MB/sec
    sample_1000             0.44s   103.44  MB/sec      0.18   252.85  MB/sec
    sample_100000           0.50s   91.02   MB/sec      0.29   156.94  MB/sec
    search                  0.59s   77.14   MB/sec      0.27   168.56  MB/sec
    select                  0.41s   111.00  MB/sec      0.14   325.09  MB/sec
    sort                    2.59s   17.57   MB/sec      2.18   20.87   MB/sec
    slice_one_middle        0.22s   206.88  MB/sec      0.08   568.92  MB/sec
    slice_one_middle_index  0.01s   4551.36 MB/sec      0.01   4551.36 MB/sec
    stats                   1.26s   36.12   MB/sec      1.09   41.75   MB/sec
    stats_index             0.19s   239.54  MB/sec      0.15   303.42  MB/sec
    stats_everything        2.13s   21.36   MB/sec      1.94   23.46   MB/sec
    stats_everything_index  1.00s   45.51   MB/sec      0.93   48.93   MB/sec

1 files changed, 15 insertions, 15 deletions

diff --git a/src/cmd/flatten.rs b/src/cmd/flatten.rs
index 918064c..12414e7 100644
--- a/src/cmd/flatten.rs
+++ b/src/cmd/flatten.rs
@@ -48,33 +48,33 @@ struct Args {
 }
 
 pub fn run(argv: &[&str]) -> CliResult<()> {
-    let args: Args = try!(util::get_args(USAGE, argv));
+    let args: Args = util::get_args(USAGE, argv)?;
     let rconfig = Config::new(&args.arg_input)
-                         .delimiter(args.flag_delimiter)
-                         .no_headers(args.flag_no_headers);
-    let mut rdr = try!(rconfig.reader());
-    let headers = try!(rdr.byte_headers());
+        .delimiter(args.flag_delimiter)
+        .no_headers(args.flag_no_headers);
+    let mut rdr = rconfig.reader()?;
+    let headers = rdr.byte_headers()?.clone();
 
     let mut wtr = TabWriter::new(io::stdout());
     let mut first = true;
     for r in rdr.byte_records() {
         if !first && !args.flag_separator.is_empty() {
-            try!(writeln!(&mut wtr, "{}", args.flag_separator));
+            writeln!(&mut wtr, "{}", args.flag_separator)?;
         }
         first = false;
-        let r = try!(r).into_iter();
-        for (i, (header, field)) in headers.iter().zip(r).enumerate() {
+        let r = r?;
+        for (i, (header, field)) in headers.iter().zip(&r).enumerate() {
             if rconfig.no_headers {
-                try!(write!(&mut wtr, "{}", i));
+                write!(&mut wtr, "{}", i)?;
             } else {
-                try!(wtr.write_all(&header));
+                wtr.write_all(&header)?;
             }
-            try!(wtr.write_all(b"\t"));
-            try!(wtr.write_all(&*util::condense(Cow::Borrowed(&*field),
-                                                args.flag_condense)));
-            try!(wtr.write_all(b"\n"));
+            wtr.write_all(b"\t")?;
+            wtr.write_all(&*util::condense(
+                Cow::Borrowed(&*field), args.flag_condense))?;
+            wtr.write_all(b"\n")?;
         }
     }
-    try!(wtr.flush());
+    wtr.flush()?;
     Ok(())
 }