Refactor code-style

*   Improve error messages somewhat
*   Clean so much stuff

.gitignore

@@ -6,3 +6,4 @@ coverage/
 *.d.cts
 *.log
 yarn.lock
+!/test/types.d.ts

doc/configure.md

@@ -21,7 +21,7 @@ is turned on, depending on the following options:
 
 In this case, the first file that is searched for in a directory is used as the
 configuration.
-If no file is found, the parent directory is searched, and so on.
+If no file is found, the parent folder is searched, and so on.
 
 ###### Example
 

doc/ignore.md

@@ -13,9 +13,9 @@ regardless of [`detectIgnore`][detect-ignore] and [`ignoreName`][ignore-name].
 Otherwise, ignore files are detected if [`detectIgnore`][detect-ignore] is
 turned on and [`ignoreName`][ignore-name] is given.
 
-The first file named `ignoreName` in the parent directory of a checked path is
+The first file named `ignoreName` in the parent folder of a checked path is
 used.
-Or, if no file is found, the parent directory if searched, and so on.
+Or, if no file is found, the parent folder if searched, and so on.
 
 ## Additional ignoring