Migrate to scalable tag bucket data structure

[chungquantin]

What is Tag Bucket?

Tag bucket stores the configuration passed into the action handler. Therefore, more databases can be supported dynamically. Opens a chance for SQL storage integration.

• Current tag allowed are: column_family which for databases with column families design. There can be tags like table for SQL table.

type TagKey = &'static str;
type TagValue = String;
type TagBucketInner = HashMap<TagKey, TagValue>;

#[derive(Clone, Default)]
pub struct TagBucket(TagBucketInner);

impl TagBucket {
	pub fn new(map: TagBucketInner) -> TagBucket {
		TagBucket(map)
	}

	pub fn get(&self, key: TagKey) -> Option<TagValue> {
		self.0.get(key).cloned()
	}

	pub fn unchecked_get(&self, key: TagKey) -> TagValue {
		self.0.get(key).unwrap().clone()
	}

	pub fn get_bytes(&self, key: TagKey) -> Option<Vec<u8>> {
		let wrapped_value = self.0.get(key).cloned();
		if let Some(v) = wrapped_value {
			return Some(v.as_bytes().to_vec());
		}
		None
	}
}