Use `eval $(resh-init)` instead of `. ~/.resh/shellrc`

[curusarn]

This way we won't need the special ~/.resh location.
It's more standard and robust.
It will help with #73

[curusarn]

We should make sure that people can still do something like this.

https://code.visualstudio.com/docs/terminal/shell-integration ->

PORTABILITY VERSUS PERFORMANCE
The recommended approach above to install shell integration relies on executing our CLI
to find the path to the shell integration script. This is great as it works cross-platform and
also with all install types, provided code in on the $PATH. This currently launches Node.js
in order to fetch the path, which can add a small delay to shell startup. To reduce this, you
can inline the script above by resolving the path ahead of time and adding it directly into
your init script.

# Output the executable's path first:
code --locate-shell-integration-path bash

# Add the result of the above to the source statement:
[[ "$TERM_PROGRAM" == "vscode" ]] && . "/path/to/shell/integration/script.sh"

[curusarn]

This should also work: source "$(resh-get-shellrc-path)"
PRO's: no eval, no need to pack shell scripts into go
CON's: resh needs to know the shellrc location, possibly slower than outputting and eval'ing the shell directly

[curusarn]

Related: #193