rhysd/hgrep v0.3.5 on GitHub

Add HGREP_DEFAULT_OPTS environment variable to set the default command line options. For example, the following configuration enables ayu-dark theme and background colors by default. See the document for more details.
```
export HGREP_DEFAULT_OPTS='--theme ayu-dark --background'
```
Detect the terminal color support from TERM environment variable in addition to COLORTERM environment variable. For example, xterm-256color enables 256 colors support. See the document to know the logic of the color support detection.
Update the themes bundle to the latest.
Update cargo dependencies including syntect v5.2.