Light-weight configuration parsing

Package config can be used to parse flags, environmental variables and configuration files, and store them in a given struct.

The priority of the sources is the following:

1. flags
2. env. variables
3. given config file
4. flag defaults
5. default config file

For example, if values from the following sources were loaded:

Defaults : {
		"user": "default",
		"secret": "",
		"endpoint": "https:localhost"
        "port": 99,
}

Given config file : {
		"user": "root"
		"secret": "confsecret"
}

Env : {
		"secret": "somesecretkey"
        "port": 88
}

Flags : {
        "port": 77 
}

The resulting config will have the following values:

	{
		"user": "root",
		"secret": "somesecretkey",
		"endpoint": "https:localhost"
        "port": 77,
	}

Supported file types

The config files may be of the following types:

• toml
• yml
• json

Keep in mind

• There is no case sensitivty, i.e. "pim", "Pim" and "PIM" are all considered the same
• The names of the environmental variables must match that of the struct. It is possible to set a prefix, so that i.e. if "MYVAR_" is set as a prefix, "MYVAR_PIM" will map to the property "pim"/"Pim"/"PIM".
• For flags to map to the config automatically they must have the same name

Currently not supported

• Anonymous structs for yaml files. Example:

type Inner struct {
	hello string
}

type Outer struct {
	Inner
	goodbye string
}

This is due to how the standard yml packages (currently) parses structs.

• Setting more complex structures via flags.

Example, in the case of this struct

type MyConfig struct {
	Debug   bool   `yaml:"debug" toml:"debug"`
	Log     string `yaml:"log" toml:"log"`

	Local struct {
		Host string `yaml:"host" toml:"host"`
		Port int    `yaml:"port" toml:"port"`
	} `yaml:"local" toml:"local"`

	Remote struct {
		Host string `yaml:"host" toml:"host"`
		Port int    `yaml:"port" toml:"port"`
	} `yaml:"remote" toml:"remote"`
}

for the flags -host / -port, the first corresponding property will be set, which in this case is the Local struct's properties.