add a little more details to execution exceptions

public/scripts/slash-commands/SlashCommandExecutionError.js

@@ -0,0 +1,60 @@
+export class SlashCommandExecutionError extends Error {
+    /**@type {string} */ commandName;
+    /**@type {number} */ start;
+    /**@type {number} */ end;
+    /**@type {string} */ commandText;
+
+    /**@type {string} */ text;
+    get index() { return this.start; }
+
+    get line() {
+        return this.text.slice(0, this.index).replace(/[^\n]/g, '').length;
+    }
+    get column() {
+        return this.text.slice(0, this.index).split('\n').pop().length;
+    }
+    get hint() {
+        let lineOffset = this.line.toString().length;
+        let lineStart = this.index;
+        let start = this.index;
+        let end = this.index;
+        let offset = 0;
+        let lineCount = 0;
+        while (offset < 10000 && lineCount < 3 && start >= 0) {
+            if (this.text[start] == '\n') lineCount++;
+            if (lineCount == 0) lineStart--;
+            offset++;
+            start--;
+        }
+        if (this.text[start + 1] == '\n') start++;
+        offset = 0;
+        while (offset < 10000 && this.text[end] != '\n') {
+            offset++;
+            end++;
+        }
+        let hint  = [];
+        let lines = this.text.slice(start + 1, end - 1).split('\n');
+        let lineNum = this.line - lines.length + 1;
+        let tabOffset = 0;
+        for (const line of lines) {
+            const num = `${' '.repeat(lineOffset - lineNum.toString().length)}${lineNum}`;
+            lineNum++;
+            const untabbedLine = line.replace(/\t/g, ' '.repeat(4));
+            tabOffset = untabbedLine.length - line.length;
+            hint.push(`${num}:  ${untabbedLine}`);
+        }
+        hint.push(`${' '.repeat(this.index - lineStart + lineOffset + 1 + tabOffset)}^^^^^`);
+        return hint.join('\n');
+    }
+
+
+
+    constructor(cause, message, commandName, start, end, commandText, fullText) {
+        super(message, { cause });
+        this.commandName = commandName;
+        this.start = start;
+        this.end = end;
+        this.commandText = commandText;
+        this.text = fullText;
+    }
+}