EduNLP v0.0.6

1. dev: add half-pretrained rnn model
2. important!!!: rename TextTokenizer to PureTextTokenizer, and add a new tokenizer named TextTokenizer (the two have similar but not the same behaviours).
3. sif: add $\textf{}$ syntax
4. add two pretrained w2v model: w2v_sci_300 and w2v_lit_300