set version to 0.23.2

Update README.md

update README for v0.23.0 to release

fix README

swith to use opengene.org/plotly-1.2.0.min.js

since the plotly.js CDN is not stable

set version to v0.20.0

fix a bug in fastareader for FASTA with space in name

revise the insert size estimation a little when trim front is enabled

support blank records

OpenGene#133

improve cut_right

OpenGene#122