Add structopt dependency in version 0.3.7

This patch series replaces argparse with structopt in the argument
handling code. As a first step, we need structopt as a dependency.

Import subrepo structopt/:structopt at efbdda4753592e27bc430fb01f7b9650b2f3174d
Import subrepo bitflags/:bitflags at 30668016aca6bd3b02c766e8347e0b4080d4c296
Import subrepo clap/:clap at 784524f7eb193e35f81082cc69454c8c21b948f7
Import subrepo heck/:heck at 093d56fbf001e1506e56dbfa38631d99b1066df1
Import subrepo proc-macro-error/:proc-macro-error at 6c4cfe79a622c5de8ae68557993542be46eacae2
Import subrepo proc-macro2/:proc-macro2 at d5d48eddca4566e5438e8a2cbed4a74e049544de
Import subrepo quote/:quote at 727436c6c137b20f0f34dde5d8fda2679b9747ad
Import subrepo rustversion/:rustversion at 0c5663313516263059ce9059ef81fc7a1cf655ca
Import subrepo syn-mid/:syn-mid at 5d3d85414a9e6674e1857ec22a87b96e04a6851a
Import subrepo syn/:syn at e87c27e87f6f4ef8919d0372bdb056d53ef0d8f3
Import subrepo textwrap/:textwrap at abcd618beae3f74841032aa5b53c1086b0a57ca2
Import subrepo unicode-segmentation/:unicode-segmentation at 637c9874c4fe0c205ff27787faf150a40295c6c3
Import subrepo unicode-width/:unicode-width at 3033826f8bf05e82724140a981d5941e48fce393
Import subrepo unicode-xid/:unicode-xid at 4baae9fffb156ba229665b972a9cd5991787ceb7

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diff --git a/heck/README.md b/heck/README.md
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+# **heck** is a case conversion library
+
+!["I specifically requested the opposite of this."](https://github.com/withoutboats/heck/blob/master/no_step_on_snek.png)
+
+This library exists to provide case conversion between common cases like
+CamelCase and snake_case. It is intended to be unicode aware, internally
+consistent, and reasonably well performing.
+
+## Definition of a word boundary
+
+Word boundaries are defined as the "unicode words" defined in the
+`unicode_segmentation` library, as well as within those words in this manner:
+
+1. All underscore characters are considered word boundaries.
+2. If an uppercase character is followed by lowercase letters, a word boundary
+is considered to be just prior to that uppercase character.
+3. If multiple uppercase characters are consecutive, they are considered to be
+within a single word, except that the last will be part of the next word if it
+is followed by lowercase characters (see rule 2).
+
+That is, "HelloWorld" is segmented `Hello|World` whereas "XMLHttpRequest" is
+segmented `XML|Http|Request`.
+
+Characters not within words (such as spaces, punctuations, and underscores)
+are not included in the output string except as they are a part of the case
+being converted to. Multiple adjacent word boundaries (such as a series of
+underscores) are folded into one. ("hello__world" in snake case is therefore
+"hello_world", not the exact same string). Leading or trailing word boundary
+indicators are dropped, except insofar as CamelCase capitalizes the first word.
+
+### Cases contained in this library:
+
+1. CamelCase
+2. snake_case
+3. kebab-case
+4. SHOUTY_SNAKE_CASE
+5. mixedCase
+6. Title Case
+
+
+### Contributing
+
+PRs of additional well-established cases welcome.
+
+This library is a little bit opinionated (dropping punctuation, for example).
+If that doesn't fit your use case, I hope there is another crate that does. I
+would prefer **not** to receive PRs to make this behavior more configurable.
+
+Bug reports & fixes always welcome. :-)
+
+### License
+
+heck is distributed under the terms of both the MIT license and the
+Apache License (Version 2.0).
+
+See LICENSE-APACHE and LICENSE-MIT for details.