Vendor dependencies for 0.3.0 release

vendor/heck/README.md

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+# **heck** is a case conversion library
+
+!["I specifically requested the opposite of this."](./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 by non-alphanumeric characters, as well as
+within those words in this manner:
+
+1. If an uppercase character is followed by lowercase letters, a word
+boundary is considered to be just prior to that uppercase character.
+2. 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 1).
+
+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. UpperCamelCase
+2. lowerCamelCase
+3. snake_case
+4. kebab-case
+5. SHOUTY_SNAKE_CASE
+6. Title Case
+7. SHOUTY-KEBAB-CASE
+8. Train-Case
+
+## MSRV
+
+The minimum supported Rust version for this crate is 1.56.0. This may change in
+minor or patch releases, but we probably won't ever require a very recent
+version. If you would like to have a stronger guarantee than that, please open
+an issue.
+
+## 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.