Validate BYMONTHDAY

[valentinbonneaud]

From the RFC, the ByMonthDay parameter can only take values in [1,31] u [-31,-1]

  The BYMONTHDAY rule part specifies a COMMA-separated list of days
  of the month.  Valid values are 1 to 31 or -31 to -1.

https://tools.ietf.org/html/rfc5545#section-3.3.10

[codecov-io]

Codecov Report

Merging #12 into master will decrease coverage by 0.01%.
The diff coverage is 83.33%.

@@             Coverage Diff              @@
##             master      #12      +/-   ##
============================================
- Coverage     98.88%   98.87%   -0.02%     
- Complexity     1870     1875       +5     
============================================
  Files            65       65              
  Lines          5307     5313       +6     
============================================
+ Hits           5248     5253       +5     
- Misses           59       60       +1

Impacted Files	Coverage Δ	Complexity Δ
lib/Recur/RRuleIterator.php	99.17% <83.33%> (-0.2%)	213 <0> (+5)

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