Provide `nocatch` keyword

A `nocatch` block is a block which may throw an exception, which is ignored (except if scream-errors is on.)

```java
nocatch {
_codeThatThrowsAnException();
}
```

is compiled to

```java
try {
_codeThatThrowsAnException();
} catch(Exception @ex) {
// Ignored
}
```

首先定位 block 关键字的 parser/compiler 入口点以及现有的 try/catch 处理。比较所请求的 nocatch 语法及其编译形式，包括 scream-errors 异常，然后找出或添加覆盖，表明异常会按指定被忽略。

由索引模型根据 Issue 内容生成。