Migrate from os.system to subprocess.Popen

[paramsiddharth]

Closes #33: Migration to "subprocess" for executing commands

Improvements:

• Uses subprocess.Popen instead of os.system for compilation and execution statements.
• In each of the child processes created, the flow of stdin and stdout are controlled i. e. Both are set in subprocess.PIPE and manually controlled using obj.stdin and obj.communicate().
• Converted all file paths into OS-agnostic paths using os.path.join. The use of '/' as a separator might cause unexpected issues in several systems; os.path takes care of that.

The problem mentioned in #31 caused by whitespaces in the directory/file names is no longer a problem after the use of subprocess. The arguments are passed as an array to subprocess.Popen, which takes care of escaping the characters in an OS-agnostic way to avoid any possible error:

...
obj = subprocess.Popen(['g++', full_filename, '-o', full_output_filename], 
                stdin=subprocess.PIPE, stdout=subprocess.PIPE)
...

The changes have been tested and Codemon successfully works in both GNU/UNIX-like (MSYS2, bash, WSL2, xterm) Windows (cmd.exe, PowerShell) environments.

[ankushbhardwxj]

@paramsiddharth - Could you reduce tabSize to 2 for all the files & use spaces instead of tabs ?

[paramsiddharth]

@paramsiddharth - Could you reduce tabSize to 2 for all the files & use spaces instead of tabs ?

Sure! Let me do it.

[paramsiddharth]

Done.

[paramsiddharth]

PR #39 has introduced conflicts to CodemonMeta.py. Let me resolve them.

[paramsiddharth]

I have resolved the conflicts. Please have a look.

[paramsiddharth]

Turns out there are still conflicts and information lost.