Custom PatternNameGenerator fields

[mschfh]

The current implementation does not seem to allow passing custom params to PatternNameGenerator, although the documentation mentions predefined names, suggesting that it is possible to add custom fields:

The pattern is like golangs fmt package (https://pkg.go.dev/fmt), but allows for named fields in curly braces. The available predefined names are:

prefix - content of the Prefix field
ext - content of the Extension field
ts - current time as 14-digit GMT Time-stamp
serial - atomically increased serial number for every generated file name. Initial value is 0 if Serial field is not set
ip - primary IP address of the node
host - host name of the node
hostOrIp - host name of the node, falling back to IP address if host name could not be resolved

Please add an exported field for custom parameters. When generating filenames, the predefined fields (prefix, ext, hostOrIp, etc.) should be always set, just changing params to an exported field would break the current default initialization logic:

gowarc/warcfile.go

Lines 86 to 94 in 2cff962

	if g.params == nil {
	g.params = map[string]interface{}{
	"prefix": g.Prefix,
	"ext": g.Extension,
	"ip": ip(),
	"host": host(),
	"hostOrIp": hostOrIp(),
	}
	}