Add space-backtick rule, default: on.

```diff
- 演示`code`代码
+ 演示 `code` 代码
```

Fix #153

autocorrect/.autocorrectrc.default

@@ -7,6 +7,8 @@ rules:
   space-punctuation: 1
   # Add space between brackets (), [] when near the CJK.
   space-bracket: 1
+  # Add space between ``, when near the CJK.
+  space-backtick: 1
   # Add space between dash `-`
   space-dash: 0
   # Convert to fullwidth.

autocorrect/src/format.rs

@@ -232,6 +232,7 @@ mod tests {
             "《腾讯》-发布-《新版》本微信" => "《腾讯》- 发布 -《新版》本微信",
             "“腾讯”-发布-“新版”本微信" => "“腾讯” - 发布 - “新版”本微信",
             "‘腾讯’-发布-‘新版’本微信" => "‘腾讯’ - 发布 - ‘新版’本微信",
+            "行内`code`代码" => "行内 `code` 代码",
         ];
 
         assert_cases(cases);

autocorrect/src/rule/mod.rs

@@ -25,6 +25,8 @@ lazy_static! {
         Rule::new("space-bracket", word::format_space_bracket),
         // Rule: space-dash
         Rule::new("space-dash", word::format_space_dash),
+        // Rule: space-backtick
+        Rule::new("space-backtick", word::format_space_backtick),
         // Rule: fullwidth
         Rule::new("fullwidth", fullwidth::format),
     ];
@@ -200,6 +202,7 @@ mod tests {
             "space-punctuation",
             "space-bracket",
             "space-dash",
+            "space-backtick",
             "fullwidth",
             "halfwidth-word",
             "halfwidth-punctuation",

autocorrect/src/rule/word.rs

@@ -32,6 +32,12 @@ lazy_static! {
         Strategery::new(r"[\]\)]", r"\p{CJK}"),
     ];
 
+    static ref BACKTICK_STRATEGIES: Vec<Strategery> = vec![
+        // Add space before and after backtick ` near the CJK
+        Strategery::new(r"\p{CJK}", r"`.+`"),
+        Strategery::new(r"`.+`", r"\p{CJK}"),
+    ];
+
     static ref DASH_RE : regex::Regex = regexp!(r"([\p{CJK}])[\-]([\p{CJK}])");
 
     static ref NO_SPACE_FULLWIDTH_STRATEGIES: Vec<Strategery> = vec![
@@ -75,6 +81,14 @@ pub fn format_space_dash(input: &str) -> String {
         .to_string()
 }
 
+pub fn format_space_backtick(input: &str) -> String {
+    let mut out = String::from(input);
+    BACKTICK_STRATEGIES
+        .iter()
+        .for_each(|s| out = s.format(&out));
+    out
+}
+
 pub fn format_no_space_fullwidth(input: &str) -> String {
     let mut out = String::from(input);
 
@@ -103,7 +117,7 @@ pub fn format_no_space_fullwidth_quote(input: &str) -> String {
 
 #[cfg(test)]
 mod tests {
-    use crate::rule::word::format_space_dash;
+    use crate::rule::word::{format_space_backtick, format_space_dash};
 
     #[test]
     fn test_format_space_bracket() {
@@ -112,4 +126,23 @@ mod tests {
         assert_eq!(format_space_dash("你好-world"), "你好-world");
         assert_eq!(format_space_dash("hello-world"), "hello-world");
     }
+
+    #[test]
+    fn test_format_space_backtick() {
+        assert_eq!(format_space_backtick("代码`code`"), "代码 `code`");
+        assert_eq!(format_space_backtick("代码`code`代码"), "代码 `code` 代码");
+        assert_eq!(
+            format_space_backtick("`code`代码`code`"),
+            "`code` 代码 `code`"
+        );
+        assert_eq!(
+            format_space_backtick("`code`hello`code`"),
+            "`code`hello`code`"
+        );
+
+        assert_eq!(format_space_backtick("```rs"), "```rs");
+        assert_eq!(format_space_backtick("``代码第1行"), "``代码第1行");
+        assert_eq!(format_space_backtick("`代码第1行"), "`代码第1行");
+        assert_eq!(format_space_backtick("代码第2行`"), "代码第2行`");
+    }
 }