This adds a `-m`/`--map-syntax` option that allows users to (re)map
certain file extensions or file names to an existing syntax.
For example:
```
bat --map-syntax .config:json
```
The option can be use multiple times. Note that you can easily make
these mappings permanent by using `bat`s new configuration file.
closes#169
This allows users to create simple configuration file
(`~/.config/bat/config` on Linux) that has the following format:
```bash
--flag1
--flag2
--option1=value1
# lines beginning with '#' are ignored
--option2=value2
# empty lines and trailing whitespace are also ignored
--option3=value3
```
* Generate shell completions with clap during build
* Updated ci release script, added SHELL_COMPLETIONS_DIR override to build.rs and fixed dependency version
