Improve configuration setting and its customization

[zaemyung]

• Currently, the configuration of sentsplit is done via dicts in config.py.
• And customizing the config setting is done as follows:

  from copy import deepcopy
  from sentsplit.config import ko_config
  from sentsplit.segment import SentSplit
  
  my_config = deepcopy(ko_config)
  my_config['segment_regexes'].append({'name': 'tilde_ending', 'regex': r'(?<=[다요])~+(?= )', 'at': 'end'})
  sent_splitter = SentSplit('ko', **my_config)
  
  sent_splitter.segment('안녕하세요~ 만나서 정말 반갑습니다~~ 잘 부탁드립니다!')
  
  # results with the regex: ['안녕하세요~', ' 만나서 정말 반갑습니다~~', ' 잘 부탁드립니다!']
  # results without the regex: ['안녕하세요~ 만나서 정말 반갑습니다~~ 잘 부탁드립니다!']

• Improve config structure so that it facilitates easier customization and maintenance.