Add ability to set only few REST methods.

[DarkSide666]

for example:
$restapi->rest('/country', new Model_Country($smbo->db), ['read']);
only will set GET methods.

Also now it supports loadBy() like this:

api/country/2 = load(2)
api/country/code:GB = loadBy('code', 'GB')
api/country/name:United%20Kingdom = loadBy('name', 'United Kingdom')
api/country/:United+Kingdom = loadBy($model->title_field, 'United Kingdom')

[codecov]

Codecov Report

Merging #6 into develop will decrease coverage by 4.81%.
The diff coverage is 2.85%.

@@              Coverage Diff              @@
##             develop       #6      +/-   ##
=============================================
- Coverage         40%   35.18%   -4.82%     
- Complexity        56       75      +19     
=============================================
  Files              1        1              
  Lines            140      162      +22     
=============================================
+ Hits              56       57       +1     
- Misses            84      105      +21

Impacted Files	Coverage Δ	Complexity Δ
src/Api.php	35.18% <2.85%> (-4.82%)	75 <28> (+19)

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[romaninsh]

good changes. but please reflect in doc (or readme)