fix: escape structured data and enforce micro precision per rfc5424

[ctrlaltf24]

• ensure timestamp's sub-seconds is no more than 6 digits of precision (by using microseconds)
  • per section 6 of rfc5424

      TIME-SECFRAC    = "." 1*6DIGIT

(also re-iterated in section 6.2.3)

   Example 5 - An Invalid TIMESTAMP

         2003-08-24T05:14:15.000000003-07:00

   This example is nearly the same as Example 4, but it is specifying
   TIME-SECFRAC in nanoseconds.  This results in TIME-SECFRAC being
   longer than the allowed 6 digits, which invalidates it.

• escape structured data values
  • per section 6.3.3 of rfc5424

   Inside PARAM-VALUE, the characters '"' (ABNF %d34), '\' (ABNF %d92),
   and ']' (ABNF %d93) MUST be escaped. 

Resolves: #73