[API] Redesign invalid record concept.

When opening a record there is a non-zero chance, that you will receive an empty record with no attributes attached. Previously it was considered as invalid record, because there was at least pid and tid attributes attached. But now seems to be there is no need to attach internal attributes before filtering. However now it is considered as valid, just without attributes.
[Unit Testing] Using unspecified bool conversion.
[Unit Testing] Wide usage of implicit bool conversion.
[Code Style] Prettifying.
[Planning] Another notice.
[Detail] Decomposing timestamp initialization.

Current timestamp value can now be initialized using free function. This change slightly reduces code dirtiness in some Logger methods.
[Planning] Notice added about unnecessary copying.
[Detail] Dealing with pid attribute.

Process id attribute initialization is now incapsulated in free function, which we use in logger internally.
[Detail] Initializers for TID and LWP attributes.
[Code Style] Style.
[Feature] Attributes attachment as a feature.

Every project should define which of internal attributes should be attached to every logging event.