fix: EfficientFrontier class was not available

EfficientFrontier class was not available through __init__.py after refactoring.

Author: chilango74

README.md

@@ -4,7 +4,7 @@
         <img src="https://img.shields.io/badge/python-v3-brightgreen.svg"
             alt="python"></a> &nbsp;
     <a href="https://pypi.org/project/okama/">
-        <img src="https://img.shields.io/badge/pypi-v0.93-brightgreen.svg"
+        <img src="https://img.shields.io/badge/pypi-v0.94-brightgreen.svg"
             alt="pypi"></a> &nbsp;
     <a href="https://opensource.org/licenses/MIT">
         <img src="https://img.shields.io/badge/license-MIT-brightgreen.svg"

okama/__init__.py

@@ -24,6 +24,7 @@
 from okama.portfolio import Portfolio
 from okama.macro import Inflation, Rate
 from okama.frontier.multi_period import EfficientFrontierReb
+from okama.frontier.single_period import EfficientFrontier
 from okama.plots import Plots
 from okama.api.data_queries import QueryData
 from okama.api.search import search
@@ -32,4 +33,4 @@
 from okama.helpers import Float, Frame, Rebalance, Date
 import okama.settings
 
-__version__ = '0.93'
+__version__ = '0.94'