logd: Allow flags "eng" and "svelte" in boolean

- enhance property_get_bool, drop property_get_bool_svelte
- enhance base properties with ro and persist variants
- update and fortify README.property
- primarily move auditd and kernel logger into a realm where
  they can be controlled by build properties.
- Move logd.klogd to logd.kernel, and add ro.logd.kernel
  and persist.logd.kernel.
- Add ro.logd.auditd and persist.logd.auditd.
- Document persist.logd.security
- Document log.tag and persist.logd.tag properties.
- Document ro.logd.size, persist.logd.size and logd.size
  properties.

Bug: 26178938
Bug: 26029733
Bug: 17760225
Change-Id: Ibc1a497e45d69db5cf52133937f7ba6fb1d6cd21