fix(build): modernize project configuration and test setup for current toolchain compatibility

ts/index.ts

@@ -19,22 +19,22 @@ export class Smartfm {
   /**
    * add frontmatter to a string
    */
-  stringify(bodyString: string, frontmatterData: any) {
+  stringify(bodyString: string, frontmatterData: Record<string, unknown>): string {
     return grayMatter.stringify(bodyString, frontmatterData);
   }
 
   /**
    * parse a string that has frontmatter attached, YAML notation
    */
-  parse(stringToParse: string) {
+  parse(stringToParse: string): grayMatter.GrayMatterFile<string> {
     return grayMatter(stringToParse);
   }
 
   /**
    * parse from comments
    */
-  parseFromComments(commentStart: string, stringToParse: string) {
-    const diffFunc = (diffMe, diffBy) => diffMe.split(diffBy).join('');
+  parseFromComments(commentStart: string, stringToParse: string): grayMatter.GrayMatterFile<string> {
+    const diffFunc = (diffMe: string, diffBy: string): string => diffMe.split(diffBy).join('');
     let lines = stringToParse.split('\n');
     lines = lines.map((line) => {
       return diffFunc(line, commentStart);