Format mgr:sbuf report as YAML

[kinkie]

No description provided.

[kinkie]

Only formatting changes were performed. A couple of keys were simplified/clarified.
Sample output from master:

These statistics are experimental; their format and contents should not be relied upon, they are bound to change as the SBuf feature is evolved
SBuf stats:
number of allocations: 6412
copy-allocations: 1347
copy-allocations from C String: 673
live references: 2027
no-copy assignments: 1201
clearing operations: 3027
append operations: 3125
move operations: 292
dump-to-ostream: 9
set-char: 1245
get-char: 393
comparisons with data-scan: 371
comparisons not requiring data-scan: 8
copy-out ops: 42
raw access to memory: 6324
NULL terminate C string: 1172
chop operations: 625
trim operations: 0
find: 60
case-change ops: 68
COW completely avoided: 689
COW replaced with memmove(3): 0
COW requiring an empty buffer allocation: 1888
COW requiring allocation and copying: 99
average store share factor: 1.55684
MemBlob created: 1988
MemBlob alive: 1295
MemBlob append calls: 2886
MemBlob currently allocated size: 62112
live MemBlob mean current allocation size: 47.9629

SBuf size distribution at destruct time:
	30-30	70
	31-32	1
	33-33	1
	37-38	2
	38-39	1
	43-45	5
	59-63	3
	97-106	1
MemBlob capacity distribution at destruct time:
	31-32	5
	63-67	1

sample output with PR applied:

SBuf stats:
  allocations: 9886
  copy-allocations: 4507
  copy-allocations from cstring: 729
  live references: 2058
  no-copy assignments: 1248
  clearing operations: 3194
  append operations: 5361
  move operations: 853
  dump-to-ostream: 108
  set-char: 1247
  get-char: 2637
  comparisons with data-scan: 642
  comparisons not requiring data-scan: 8
  copy-out ops: 9
  raw access to memory: 8549
  NULL terminate cstring: 1174
  chop operations: 5047
  trim operations: 0
  find: 1281
  case-change ops: 68
  COW completely avoided: 723
  COW replaced with memmove: 0
  COW requiring an empty buffer allocation: 2064
  COW requiring allocation and copying: 170
  average store share factor: 1.549
MemBlob stats:
  allocations: 2235
  live instances: 1322
  append calls: 4071
  cumulative size bytes: 63296
  mean size: 47.9
SBuf size distribution at destruct time:
  30-30: 70
  31-32: 1
  33-33: 1
  37-38: 2
  38-39: 1
  43-45: 5
  59-63: 3
  97-106: 1
MemBlob capacity distribution at destruct time:
  31-32: 5
  63-67: 1

[kinkie]

StatHist has a definitely dated API, but this is not the PR to change that.
My goal for this sprint is to get to convert all cachemgr reports to yaml

[rousskov]

Please wait for spaces() issue to be resolved before posting more YAML PRs or requesting additional reviews.

[rousskov]

Please do not use std::string in primary Squid code. In most cases (probably including this one), using SBuf is best. I am aware that this code reports SBuf stats.