Can't use master branch with pip installation

Hi! This is a follow-up of the discussion in #229: basically if I install `mssql-cli` latest stable release with pip by doing
```
pip install --user mssql-cli
```
then I can connect to a db by running something like `mssql-cli -S host -U user -P password` without any problems. However when I install the latest (master) version by virtue of
```
pip install --user git+https://github.com/dbcli/mssql-clii
```
then the package is correctly installed but when attempting to connect to a database I get:
```
Traceback (most recent call last):
File "/home/pedro/.local/bin/mssql-cli", line 10, in
sys.exit(main())
File "/home/pedro/.local/lib/python3.7/site-packages/mssqlcli/main.py", line 93, in main
run_cli_with(mssqlcli_options)
File "/home/pedro/.local/lib/python3.7/site-packages/mssqlcli/main.py", line 51, in run_cli_with
mssqlcli = MssqlCli(options)
File "/home/pedro/.local/lib/python3.7/site-packages/mssqlcli/mssql_cli.py", line 191, in __init__
self.sqltoolsclient = SqlToolsClient(enable_logging=options.enable_sqltoolsservice_logging)
File "/home/pedro/.local/lib/python3.7/site-packages/mssqlcli/sqltoolsclient.py", line 34, in __init__
sqltoolsservice_args = [mssqltoolsservice.get_executable_path()]
File "/home/pedro/.local/lib/python3.7/site-packages/mssqlcli/mssqltoolsservice/__init__.py", line 31, in get_executable_path
raise EnvironmentError(error_message)
OSError: /home/pedro/.local/lib/python3.7/site-packages/mssqlcli/mssqltoolsservice/bin/MicrosoftSqlToolsServiceLayer does not exist. Please re-install the mssql-cli package
Exception ignored in:
Traceback (most recent call last):
File "/home/pedro/.local/lib/python3.7/site-packages/mssqlcli/mssql_cli.py", line 196, in __del__
if self.sqltoolsclient:
AttributeError: 'MssqlCli' object has no attribute 'sqltoolsclient'
```

Reproduce las dos rutas de instalación y, después, inspecciona mssqlcli/main.py, mssqlcli/mssql_cli.py, mssqlcli/sqltoolsclient.py y mssqlcli/mssqltoolsservice/__init__.py, especialmente cómo se empaqueta y se localiza el ejecutable de SQL Tools Service. Se considera terminado cuando una instalación de la rama master incluye el ejecutable y puede conectarse usando el comando mssql-cli indicado sin el traceback.

Escrito por el modelo de indexación a partir del texto del issue.