Improve Gromacs input parameter parsing further

[JFRudzinski]

in #122 we already made some serious improvements to str_to_input_parameters(), but there are still some issues:

1. The approach may be able to be improved:

@ladinesa suggested:

re_section = re.compile(r'(?P<indent> +?)(?P<key>\S+?) +\(*(?P<index>\d*)\)*\:')
re_value = re.compile(r'(?P<indent> +?)(?P<key>\S+?) *[:=]+ *(?P<value>[^\n]+)')

converters = [
    (re.compile(r'([-+]?\d+)'), lambda x: int(x.group(1))),
    (re.compile(r'(?i:(?:true|false))'), lambda x: x.group(1).lower() == 'true'),
    (re.compile(r'([-+]?\d+\.*\d*(?:[Ee][-+]\d+)?)'), lambda x: float(x.group(1))),
    (re.compile(r'\{(\d+),\.\.\.,(\d+)\}'), lambda x: list(range(int(x.group(1)), int(x.group(2))))),
    (re.compile(r'\{*([\d\.]+,.+)\}*'), lambda x: [float(v) for v in x.group(1).split(',')])
]

def convert_value(value):
    value = value.strip()
    for pattern, converter in converters:
        match = pattern.match(value)
        if match:
            return converter(match)
    if value.lower() == 'not available':
        return None
    return value

def parse_indented(block):
    root = {}
    stack = [(root, -1)]

    for line in block.splitlines():
        match = re_section.match(line)
        if not match:
            match = re_value.match(line)
        if not match:
            continue

        match_dct = match.groupdict()
        indent = len(match_dct.get('indent'))
        key = match_dct.get('key')
        value = match_dct.get('value')

        while stack and stack[-1][1] >= indent:
            stack.pop()

        parent = stack[-1][0]

        child = convert_value(value )if value else {}
        if key in parent:
            if isinstance(parent[key], list):
                parent[key].append(child)
            else:
                parent[key] = [parent[key], child]
        else:
            parent[key] = child

        stack.append((child, indent))
    return root

but I was not yet able to get this working completely.

2. There are some special cases, e.g., all-lambas where the indentation method fails due to length of the keyword. These exceptions need to be dealt with specially.