WIP : Unicode characters

Implements interpretation of characters by 'longname' or character codes:

    In[1]:= \[Alpha]\[Beta]\[Gamma]      (* Symbol from longname characters *)
    Out[1]= αβγ

    In[2]:= "1 \[CirclePlus] 2 "\[Integral]"      (* String from longname characters *)
    Out[2]= 1 ⊕ 2  ∫

    In[3]:= "\.78\.79\.7A\:0078\:0079\:007A\101\102\103\061\062\063" (* String from character codes *)


    In[4]:= \[Alpha] = 4;
    In[5]:= \[Alpha] + x + \[Beta]
    Out[6]= 4 + γ

    In[7]:= \[Lambda][x_]:= x^2
    In[8]:= λ[10]
    Out[8]= 100